Stepping motor control method and disk drive apparatus

ABSTRACT

In a method of the present invention for controlling stepping motor, the stepping motor driving current is increased or reduced at a fixed inclination in proportion to the time to control the stepping motor effectively, and, a stepping motor driving current pattern is changed by 1/4 cycle or over to synchronize the state of excitation between the stepping motor driving means and the stepping motor to control the pick-up very accurately. In addition, the disk apparatus of the present invention, which uses a stepping motor is provided with a pulse rate pattern variable means, a pulse rate change proportion measuring means, and a driving voltage variable means, and when the pulse rate and the pulse rate change proportion are low, the driving voltage amplitude is lowered to reduce surplus torque generation in the stepping motor.

BACKGROUND OF THE INVENTION

The present invention relates to a method for controlling steppingmotors and a disk apparatus that uses a stepping motor.

In recent years, high speed accessing performance is required for diskapparatuses to feed the pick-up to a target position on the diskquickly. A disk apparatus that uses a stepping motor as a traverse motorfor feeding the pick-up is already commercialized. Since the steppingmotor is rotated in units of a constant basic step angle in response tothe driving pulses, it is easy to open-control a strokes for feeding thepick-up and it needs no position detecting means. When using such astepping motor for a disk apparatus, therefore, the pick-up feedingmechanism can be simplified.

However, disk apparatuses that use such a conventional stepping motorrespectively have been confronted with various problems as describedbelow. An object of the present invention is to solve such problems andprovide a method for controlling stepping motors at high speeds and veryaccurately in an open-control that uses no detector such as a positionsensor, as well as to provide a disk apparatus that uses theabove-mentioned method for controlling stepping motors.

Next, various problems that will arise in disk apparatuses that use aconventional stepping motor respectively will be described in detail.

[Problems at Driving Operation of the Conventional Stepping Motors]

Hereunder, a conventional disk apparatus and a conventional method forcontrolling stepping motors will be explained with reference to theattached drawings. FIG. 54 is a schematic illustration for aconfiguration of the conventional disk apparatus. In FIG. 54, a lens 107b is held by springs 107 c and 107 d above a pick-up 107 a. Therotational movement of a stepping motor 107 f is transmitted to thepick-up 107 a via a feed screw 107 e. The pick-up 107 a makes a linearmotion in the radial direction of a disk 107 j. The disk 107 j storesinformation on its helically-formed tracks and the rotation speed of thedisk 107 j is controlled by a spindle motor 1071. Error signals from thepick-up 107 a are transmitted to a servo means 107 g. And, the servomeans 107 g outputs a signal for controlling the springs 107 c and 107 dto the pick-up 107 a so that each error signal is cleared to 0. A systemcontroller 107 i, which is connected to the servo means 107 g, aninterface means 107 k, and the spindle motor 1071, transmits a drivingcommand signal for feeding the pick-up 107 a to the stepping motorcontrolling means 107 h as needed. By receiving the driving commandsignal, the stepping motor controlling means 107 h controls the steppingmotor 107 f.

When in recording or playing back information in or from theconventional disk apparatus, the lens 107 b keeps following up thehelically-formed tracks on the disk 107 j and the lens 107 b changes itsposition gradually in the radial direction of the disk 107 j. The servomeans 107 g detects each of such displacement values of the lens 107 b.When the system controller 107 i detects that the lens 107 b hasexceeded a specified displacement value, the system controller 107 itransmits a driving command signal to the stepping motor controllingmeans 107 h. By receiving the driving command signal, the stepping motorcontrolling means 107 h rotates the stepping motor 107 f step by step atfine pitches. The stepping motor controlling means 107 h moves thepick-up 107 a by a fine distance in the radial direction of the disk 107j to limit the displacement of the lens 107 b within a low value. Then,the stepping motor 107 f is kept at rest until the lens 107 b exceedsthe specified displacement value again.

As a means of moving the pick-up by rotating the stepping motor step bystep at fine pitches, a controlling method referred to as micro-stepdriving operation is well known. The conventional micro-step drivingmethod divides the basic step angle of the stepping motor into n angles(n: an integer of 2 or over) like an optical disk apparatus disclosed,for example, in Unexamined Published Japanese Patent ApplicationPublication No. 7-272291 and changing the driving current step by step.

Next, the conventional stepping motor controlling method will beexplained.

FIG. 55 is a schematic inner configuration of a general stepping motor.In FIG. 55, a numeral 106 a indicates a current flowing in an A-phasecoil and 106 b indicates a current flowing in a B-phase coil. A rotator106 c has some pairs of N and S magnetic poles. The number of magneticpole pairs differ among types of stepping motors. A point P on therotator begins rotating when the current 106 a flowing in the A-phasecoil and the current 106 b flowing in the B-phase coil are changedtogether. The point P stops when the balance between the magnetic forcegenerated from those coils and the frictional load of rotation isstabilized. Positions 106X and 106Z indicate two points of somemechanical stability points existing on the rotator. Those two pointsare adjacent with each other. The rotation angle from the position 106Xto the position 106Z is defined as the basic step angle of the steppingmotor. The position 106Y indicates one of mechanical instability pointsexisting between the positions 106X and 106Z. To rotate the steppingmotor by a micro-step, the rotator 106 c must be rested at a mechanicalinstability position in the range of the basic step angle, as shown withthe position 106Y.

Next, the current flowing in each of the A-phase and B-phase coils ofthe stepping motor will be explained. FIG. 56 is a wave form chartindicating the driving current of the conventional stepping motor. Thewave form chart shown in FIG. 56 indicates a wave form of the current inthe controlling method referred to as a 1-2-phase exciting system thatdivides the basic step angle of the stepping motor into two angles androtating the stepping motor in units of a 1/2 step angle. There is alsoanother well-known controlling method, in which the basic step angle ofthe stepping motor is furthermore divided into n angles (n: an integerof 2 or over) and the stepping motor is rotated in units of a 1/n stepangle. To make it easier to understand the explanation here, a methodfor controlling stepping motors with a driving current as shown in FIG.56 will be picked up. The method divides the basic step angle into twoangles, which is the least division number in the controlling methods,each of which divides the basic step angle of the stepping motor into nangles.

In FIG. 56, the wave form 105 a is a driving current wave formrepresenting the flow rate and direction of the current flowing in theA-phase coil of the stepping motor on the time axis. The wave form 105 bis a driving current wave form representing the flow rate and directionof the current flowing in the B-phase coil of the stepping motor on thetime axis. In the driving current wave forms 105 a and 105 b, thecurrent flowing forward is represented by a positive value and thecurrent flowing reversely is represented by a negative value. Thecurrent wave form, when the stepping motor is rotated forward, ischanged from left to right in FIG. 56. The current wave form, when thestepping motor is rotated reversely, is changed from right to left inFIG. 56. If the current state is changed from 105X to 105Z in FIG. 56,it means that the state 105Y exists between those states. In the state105Y, only the A-phase coil shown in FIG. 55 is excited and the B-phasecoil is not excited. Thus, the stepping motor can stop at the position106Y between the positions 106X and 106Z in FIG. 55. This means that themotor can stop at 1/2 of the basic step angle of the stepping motor.Since the basic step angle of the stepping motor is divided into nangles such way, the stepping motor can be rotated step by step at finepitches. And, when using such a stepping motor for feeding the pick-upof a disk apparatus, the pick-up can be fed in micro steps in the radialdirection of the disk in a recording/playback operation.

However, the conventional stepping motor controlling method and theconventional disk apparatus have the following problems.

One of the problems is that when a stepping motor is rotated by a finestep, the pick-up is accelerated significantly. In the case of thestepping motor driving current wave form shown in FIG. 56, when thestepping motor is rotated by a fine step, the state of the steppingmotor driving current is changed in steps, for example, from 105X to105Y in a moment. At this time, a large start-up torque is generated inthe stepping motor and the pick-up is accelerated suddenly.Consequently, the lens of the pick-up is shaken, causing a light spot ofthe laser beam to be shifted from the target track on the disk. Thisresults in an off-track error. When the off-track value is great, datacannot be recorded correctly when in recording and when in playing back,the error rate is raised.

There is another problem that arises when the stepping motor type and/orany pick-up feeding mechanism specification is changed after a steppingmotor controlling method is designed. Since the stepping motor drivingcurrent wave form is fixed, the rotation value of the stepping motorcannot be adjusted. If any design is changed as mentioned above, thebalance between the torque generated in the stepping motor and thefrictional load of the pick-up feeding mechanism is lost. Consequently,the rotator of the stepping motor cannot be stopped accurately at amechanical instability position between the basic step angles, so that abig stepping motor rotation angle error occurs. Such a rotation angleerror results in an error of the pick-up feeding distance.

If the pick-up keeps following up the helically-formed tracks of thedisk when in recording or playing back as explained above, the lens ofthe pick-up is displaced gradually in the radial direction of the disk.In order to suppress the displacement of the lens as less as possible,the stepping motor must be rotated in fine steps to move the wholepick-up in fine steps in the radial direction of the disk. When a bigerror occurs in the pick-up feeding distance, it becomes difficult tomove the pick-up to cover the displaced distance of the lens. If thepick-up is moved by a distance differently from a displaced distance ofthe lens, the lens which follows up the track of the disk is alsodisplaced significantly in the pick-up. And accordingly, the focus servoand tracking servo characteristics are degraded, causing a focus jumpand/or an tracking-off error.

Furthermore, there will also arise another problem that the steppingmotor itself generates heat and this results in a wasteful powerconsumption. This is because a current keeps flowing in the coils of thestepping motor even after the stepping motor is rested.

[Problems to Occur in the Conventional Stepping Motor During Operation]

In the case that a position detecting means, such as encoder, sensor orthe like is not provided in a stepping motor, the stepping motor initialstatus, that is, the rest position of the stepping motor rotator isunknown before the stepping motor is excited.

In addition, when the stepping motor is in a step-out during rotation,the position of the stepping motor rotator becomes unknown. The step-outmeans a state of abnormal rotation of the rotator of a stepping motor,when the rotation goes out of synchronism with changes of the drivingsignal for the stepping motor.

When the position of the rotator of the stepping motor is unknown, thestepping motor is excited, then the initial position of the rotator ofthe stepping motor does not always come to a stability point ofexcitation. And, if the initial position and a stability point are notsynchronized, the rotator of the stepping motor is not rotated smoothlyand it might be moved suddenly to a stability point for the excitation.

In the case that the tracking servo of the disk apparatus is performedwhen the rotator of the stepping motor is moved suddenly to a stabilitypoint for the excitation, the pick-up and the magnetic head of the diskapparatus are also moved suddenly in the radial direction of the disk,so that they cannot follow up the tracks of the disk, causing anoff-track in some cases. When the off-track value is great, data cannotbe recorded accurately when in recording, and the error rate of theplayback data is raised when in playing back.

Furthermore, in the case that the focus servo of the disk apparatus isperformed when the rotator of the stepping motor is moved suddenly to astability point for the excitation, then the pick-up of the diskapparatus is moved suddenly in the radial direction of the disk.Consequently, the lens of the pick-up is moved significantly, therebycausing the focus servo operation to be unstable and recording/playbackof data to be disabled.

[Track Accessing Problems in Controlling of the Conventional SteppingMotor]

Next, the conventional disk apparatus will be explained with referenceto the attached drawings. FIG. 57 is a block diagram for a configurationof the conventional disk apparatus. FIG. 58 is a wave form chartindicating the relationship with respect to the time among frequencychange wave form (pulse rate pattern), generated torque, and necessarytorque of the conventional driving pulse when in continuous rotation ofthe stepping motor in order to feed the pick-up 303 fast.

In FIG. 57, the disk 301 is a recording medium provided withhelically-formed information tracks. The spindle motor 302 is providedto rotate the disk 1. The pick-up 303 is moved in the radial directionof the disk 301 due to the rotation of the stepping motor 307. Thepick-up 303 is provided with a lens 304.

This lens 304 can be moved both vertically and horizontally by operatingmagnetically a focus actuator and a tracking actuator (both notillustrated) incorporated in the pick-up 303. The focus servo means 305drives the focus actuator so that the lens is kept away by a fixeddistance from the disk 301 according to the focus error signal, which isa displacement distance from the disk 301. The tracking servo means 306drives the tracking actuator so that the lens 304 keeps following up agiven track on the disk 301 according to the tracking error signal,which is a displacement distance from the track on the disk 301.

The stepping motor 307 moves the pick-up 303. The stepping motor drivingmeans 308 applies a driving voltage to the stepping motor 307. Thepick-up position detecting means 309 detects the current position of thepick-up 303 from the address information included in the data read bythe pick-up 303. The pulse counting means 310 counts the number ofpulses for driving the stepping motor 307 to move the pick-up 303 fromthe current position detected by the pick-up position detecting means309 to a target address entered from external. The pulse rate patterncreating means 311 generates a frequency change (pulse rate pattern) ofthe pulses entered to the stepping motor driving means 308 according tothe number of pulses counted by the pulse counting means 310. The feedscrew 312 holds the pick-up 303 movably in the radial direction of thedisk 301 and transmits a rotational force of the stepping motor 307 tothe pick-up 303.

Next, the operation of the conventional disk apparatus formed asexplained above for moving the pick-up fast will be explained.

The lens 304 is driven by an electromagnetic actuator (not illustrated)to read information from the disk 301 via the pick-up 303. This lens 304is controlled by the focus servo means 305 so as to be kept focused onthe disk 301. In addition, the lens 304 is also controlled by thetracking servo means 306 so as to keep following up the tracks on thedisk 301. When accessing a given track, at first, the pulse countingmeans 310 counts the number of pulses for moving the pick-up 303 fromthe current position detected by the pick-up position detecting means309 to the target track.

Next, the stepping motor driving means 308 drives the stepping motor 307at a pulse rate as shown in (a) of FIG. 58 generated by the pulse ratepattern creating means 311 to move the pick-up 303 while the operationof the tracking servo means 306 stops. After the movement, the trackingservo means 306 is restarted to record/play back information. Theconventional disk apparatus is formed such way. The pulse rate patternshown in (a) of FIG. 58 is output as explained below from the pulse ratepattern creating means 311 being comprised of a microcomputer, etc.

The pulse rate for starting up the stepping motor 307 is a frequencythat can start up the stepping motor 307 without causing any step-out. Astep-out means a state of abnormal rotation of the rotator of a steppingmotor 307, caused when the stepping motor goes out of step with theinput pulse rate. When the stepping motor 307 is started up, the pulserate is raised at a fixed change rate up to a specified frequency. Aftera fixed pulse rate is kept for a specified time, the pulse rate islowered symmetrically to the pulse rate pattern when it was raised, tostop the pulse output.

There is another conventional stepping motor controlling method, whichis well known as a micro-step driving method in which the basic angle ofthe stepping motor is divided into n angles (n: an integer of 2 or over)and the positioning resolution of the stepping motor is multiplied by n.

Next, the stepping motor driving means will be explained. Theabove-mentioned conventional micro-step driving method is adopted forthe driving means.

FIG. 59 is a schematic illustration for an internal structure of ageneral stepping motor. In FIG. 59, 310 a indicates a voltage applied tothe A-phase coil and 310 b indicates a voltage applied to the B-phasecoil. The rotator 310 c has a plurality of pairs of N and S magneticpoles. This number of magnetic poles differ among types of steppingmotors. When the voltages 310 a and 310 b applied to the A-phase andB-phase coils are changed, the point P on the rotator begins arotational motion. The point P stops at a point where the balancebetween the magnetic force generated from the coils and the frictionalload of rotation is stabilized, that is, at a mechanical stabilityposition.

In FIG. 59, positions 310X and 310Z indicates two points of somemechanical stability points existing on the rotator 310 c. Those twopoints are adjacent with each other. The rotation angle from theposition 310X to the position 310Z is defined as the basic step angle ofthe stepping motor. The position 310Y indicates one of mechanicalinstability points existing between the positions 310X and 310Z. Torotate the stepping motor by a micro-step, the rotator 310 c must berested at a mechanical instability position in the range of the basicstep angle as shown with the position 310Y.

Next, the voltage applied to each of the A-phase and B-phase coils ofthe stepping motor will be explained.

FIG. 60 is a wave form chart indicating the driving voltage of theconventional stepping motor. The wave form chart shown in FIG. 60indicates a wave form of the voltage used in the controlling methodreferred to as a 1-2-phase exciting system that divides the basic stepangle of the stepping motor into two angles and rotating the steppingmotor in units of a 1/2 step angle. There is also another well-knowncontrolling method, in which the basic step angle of the stepping motoris furthermore divided into n angles (n: an integer of 2 or over) andthe stepping motor is rotated in units of a 1/n step angle. To make iteasier to understand the explanation here, a method for controllingstepping motors by dividing the basic step angle into two angles will beexplained hereafter. This method is the least division number, in thecontrolling methods, each of which divides the basic step angle of thestepping motor into n angles.

In FIG. 60, the wave form 311 a is a driving voltage wave formrepresenting the voltage applied to the A-phase coil of the steppingmotor on the time axis. The wave form 311 b is a driving voltage waveform representing the voltage applied to the B-phase coil of thestepping motor on the time axis. In FIG. 60, however, when the steppingmotor driving voltage applied to each of the A-phase and B-phase coilsis in the state 311X, the point P shown in FIG. 59 is assumed to be atthe position 310X. In the same way, when the voltage is in the state311Y, the point P is assumed to be positioned at 310Y and when thevoltage is in the state 311Z, the point P is assumed to be positioned at310Z.

The voltage wave form, when the stepping motor is rotated forward, ischanged from left to right in FIG. 60. When the stepping motor isrotated reversely, the voltage wave form is changed from right to leftin FIG. 60.

If the voltage state is changed from 311X to 311Z in FIG. 60, it meansthat the state 311Y exists between those states. In the state 311Y, onlythe A-phase coil shown in FIG. 59 is excited and the B-phase coil is notexcited. Thus, the point P shown in FIG. 59 can be moved to the position311Y between the positions 311X and 311Z in FIG. 59. This means that themotor can be moved to a position by 1/2 of the basic step angle of thestepping motor. Since the basic step angle of the stepping motor isdivided into n angles such way, the stepping motor can be rotated stepby step at fine pitches. And, when using such a stepping motor forfeeding the pick-up of a disk apparatus, the pick-up can be fed in microsteps in the radial direction of the disk during a recording/playbackoperation or during accessing a given track.

The configurations of such the conventional stepping motor and theconventional disk apparatus have been confronted with the followingproblems when in accessing a given track, however.

Hereunder, one of such the conventional problems will be explained. Astepping motor as shown in (a) of FIG. 58 is driven at a pulse ratehaving a trapezoidal profile in shape. Since the pulse rate is raised ata fixed change rate in the initial stage of stepping motor driving, theacceleration torque of the stepping motor is fixed at that time.However, the torque characteristics of the stepping motor have a curveshown with a broken line in (b) of FIG. 58. Thus, as shown in (b) ofFIG. 58, a surplus torque unnecessary for moving the pick-up exists inthe initial stage of stepping motor driving. This surplus torque causesthe stepping motor to vibrate during rotation. And, this vibration istransmitted to the pick-up via the feed screw, causing the controllingof the lens to be unstable. In the worst case, this vibration causesfocus jumping and tracking-off errors. In addition, such a surplustorque causes a surplus current to flow in the coils and such a surpluscurrent causes heat to be generated in the stepping motor. Those are theproblems arising from the conventional stepping motor.

Next, the vibration caused by such a surplus torque in theabove-mentioned conventional example will be explained in detail.

FIG. 61 is a wave form chart indicating time-series changes of thevoltages applied to the A-phase and B-phase coils of the stepping motor,as well as the displacement of the rotation angle of the stepping motor.In (a) of FIG. 61, the wave forms 312 a 1, 312 a 2, and 312 a 3 indicatethe voltages applied to the A-phase coil. In (b) of FIG. 61, the waveforms 312 b 1, 312 b 2, and 312 b 3 indicate the voltages applied to theB-phase coil. In (c) of FIG. 61, the wave form 312 c 1 indicates therotation angle displacement of the stepping motor when the voltages ofthe wave forms 312 a 1 and 312 b 1 are applied to the A-phase andB-phase coils respectively. In the same way, the wave form 312 c 2indicates the rotation angle displacement of the stepping motor when thevoltages of the wave forms 312 a 2 and 312 b 2 are applied to theA-phase and B-phase coils respectively. The wave form 312 c 3 indicatesthe rotation angle displacement of the stepping motor when the voltagesof the wave forms 312 a 3 and 312 b 3 are applied to the A-phase andB-phase coils respectively.

In (a) and (b) of FIG. 61, 312X, 312Z, and 312W indicate voltage-appliedstates in each of the coils of the stepping motor respectively. Each of(a) and (b) of FIG. 61 indicates a combination of voltages applied toeach of the A-phase and B-phase coils in each of the voltage-appliedstates 312X, 312Z, and 312W.

As shown in (a) and (b) of FIG. 61, if the voltage applied to each ofthe A-phase and B-phase coils of the stepping motor is in thevoltage-applied state 312X shown on the left end, the target rotationangle of the stepping motor is positioned as shown with the line 312X in(c) of FIG. 61. In the same way, if the voltage applied to each of theA-phase and B-phase coils of the stepping motor is in thevoltage-applied state 312Z, the target rotation angle of the steppingmotor is positioned as shown with the line 312Z in FIG. 61(c). And, ifthe voltage applied to each of the A-phase and B-phase coils of thestepping motor is in the voltage-applied state 312W shown on the leftend, the target rotation angle of the stepping motor is positioned asshown with the line 312W in FIG.(c) of FIG. 61. In the voltage-appliedstate 312X, however, the rotation angle of the stepping motor is assumedto be stopped at 312X.

In (a) and (b) of FIG. 61, since each period in the voltage appliedstates 312X, 312Z, and 312W indicates a pulse cycle, the reciprocalnumber of this cycle is a pulse rate. When the stepping motor is driven,a difference is generated in the rotation matching with the targetrotation angle of the stepping motor as shown in (a) and (b) of FIG. 61due to the difference between the voltages applied to the A-phase andB-phase coils, that is, the difference between the generated torques.When the voltages applied to the A-phase and B-phase coils have the waveforms 312 a 1 and 312 b 2 respectively, the rotation angle of thestepping motor is vibrated significantly as shown in the wave form 312 c1. This is because an excessive torque is generated with respect to thepulse rate, that is, the rotation speed of the stepping motor.

On the contrary, if the generated torque is too small, for example, whenthe voltages applied to the A-phase and B-phase coils have the waveforms 312 a 3 and 312 b 3 respectively, the rotation angle of thestepping motor is changed to the next voltage-applied state before therotation angle is displaced to the target one, as shown in the wave form312 c 3. Thus, the stepping motor rotation will not be synchronized withthe input driving pulses. In the worst case, the stepping motor causes astep-out and it is stopped.

On the other hand, if an optimal torque is generated with respect to thepulse rate, for example, if the voltages applied to the A-phase andB-phase coils have the wave forms 312 a 2 and 312 b 2 respectively, therotating angle of the stepping motor enters the next voltage-appliedstate as shown with the wave form 312 c 2 when the rotating angle isdisplaced almost to the target one. The stepping motor is thus rotatedsmoothly.

Next, another problem that will arise in the conventional art steppingmotor when in accessing a given track will be explained.

If, when the stepping motor is driven in micro-steps as shown in FIG.60, the positioning resolution of the stepping motor is multiplied by n,then a torque change occurs. And, as shown in FIG. 60, if both A-phaseand B-phase coils are excited into the states 311X and 311Z respectivelyin the range of the basic step angle, a fixed voltage is applied to bothA-phase and B-phase coils and the rotator is positioned at a mechanicalstability point. If the A-phase and B-phase coils are excited into thestate 311Y, however, a fixed voltage is applied only to the A-phase coiland the voltage of the B-phase coil thus becomes 0. And, the rotator ispositioned at a mechanical instability point.

When the rotator is positioned at a mechanical stability point, which isin the range of the basic step angle, as explained above, comparativelya large torque is generated. If the rotator is positioned at amechanical instability point, however, the torque becomes lower thanthat taken when the rotator is positioned in the range of the basic stepangle. Such way, the generated torque differs between when the rotatoris positioned in the range of the basic step angle and when it ispositioned at a mechanical instability point outside the range of thebasic step angle. Consequently, the vibration of the stepping motor isfurther increased during a movement of the pick-up. In the worst case,the stepping motor is in the loss of synchronism.

If the rotator moves the pick-up 303 (FIG. 57) to be at a mechanicalinstability position, only one phase is driven when the pick-up 303stops. Thus, the torque is in low and the pick-up 303 cannot be stoppedaccurately.

[Problems in the Conventional Stepping Motor Driving Mechanism]

In recent years, as a mass volume of computer programs or data isexpanded more and more in scale, the use of optical disks having alarger capacity respectively is widely spread as recording or supplymedia of software instead of conventional floppy disks. And, functionsfor high speed accessing of data on such optical disks are required forthose disk apparatuses. In order to make accessing faster, the pick-upmust be moved to a target position quickly on the optical disk. When thepick-up is accelerated/decelerated suddenly, however, problems that therack teeth are disengaged from the thread groove of the feed screw orvibration is generated in the pick-up arise. Consequently, an accessingmechanism that can be slid stably when the pick-up isaccelerated/decelerated suddenly is indispensable to make such accessingoperations faster.

Next, problems that will arise in the conventional disk apparatus whenthe pick-up is accelerated/decelerated suddenly will be explained.

Hereunder, an embodiment of the conventional disk apparatus will beexplained with reference to the attached drawings.

FIG. 62 is a perspective view of the first example of the conventionaldisk apparatus. In FIG. 62, a pick-up 202 provided with a lensreads/writes signals from/on a disk 201. The pick-up 202 is provided inthe pick-up base 203. A traverse motor 204 moves the pick-up base 203 inthe radial direction of the disk 201. A feed screw 205 is rotated by therotation of the traverse motor 204. On the outer periphery of the feedscrew 205 is formed a thread groove 215. A rack 208, fixed to thepick-up base 203, is engaged with the feed screw 205. In the rack 208are provided a fixing portion 206 to be fixed to the pick-up base 203and a nut portion 207 fit in the thread groove 215. On this nut portion207 is formed teeth 223 fit in the thread groove 215. A rack spring 224is pressing the teeth 223 against the thread groove 215.

As shown in FIG. 62, the pick-up base 203 is guided by a guidingmechanism 211 slidably in the radial direction of the disk 201. Thepick-up base 203 is provided with a guide hole 212 and the first guideshaft 209 fit in the guide hole 212 is guiding the pick-up base 203slidably in the radial direction of the disk 201. On e pick-up base 203is also formed a guide groove 213. The second guide shaft 210 is fit inthe guide groove 213 an d used to limit the rotation of the pick-up base203 around the guide shaft 209.

FIG. 63 is a side view (a) and a top view (b) of expanded portions inthe neighborhood of both feed screw 205 and rack 208.

The fixing portion 206 and the nut portion 207 of the rack 208 areconnected to a plate spring 214. Usually, the plate spring 214 is formedthinner than the nut portion 207. This is because when the movement ofthe pick-up base 203 is blocked by something, the plate spring 214 mustbe bent, so that the nut portion 207 can be released from the threadgroove 215.

In the conventional disk apparatus formed as explained above, when thetraverse motor 204 is rotated to accelerate/decelerate the pick-up basesuddenly, the first problem that the nut portion 207 of the rack 208 isdisengaged from the thread groove 215 of the feed screw 205 arises.

Furthermore, when the pick-up base 203 is accelerated/deceleratedsuddenly, the second problem that the pick-up base 203 is vibratedsignificantly arises.

Next, how the first problem will arise will be explained with referenceto FIG. 63.

When the rotation of the feed screw 205 is accelerated/decelerated, theresponse of the pick-up base 203 to the rotation is delayed due to theinertia. Consequently, the inertia working on the pick-up base 203 isapplied to the nut portion 207 via the surface of the thread groove 215.At this time, the direction of the force applied to the nut portion 207can be resolved into 3 directional components that are orthogonal toeach other; the axial direction of the feed screw 205, the radialdirection of the feed screw 205 at a point where the thread groove 215is in contact with the teeth 223 of the rack, and the tangentialdirection. Of those 3 directional components, especially the componentof the tangential direction of the feed screw acts to shift the nutportion 207 from the thread groove 215. If this shifting force is great,the nut portion 207 is twisted and the teeth 223 go off the threadgroove 215 easily. This component of the tangential direction of thefeed screw 205 becomes significant when the rotation of the feed screw205 is accelerated/decelerated suddenly or the feeding value of the feedscrew per rotation is increased significantly to move the pick-up 202fast. As a result, the teeth 223 go off the thread groove 215 easily.

In the conventional rack 208 as shown in FIG. 63, the nut portion 207 issupported only by a plate spring 214 whose rigidity is low. Thus, thenut portion 207 cannot secure a rigidity enough especially to cope withthe component of the force working in the tangential direction of thefeed screw 205. In the conventional disk apparatus in the statusmentioned above, therefore, the nut portion 207 is deformed like beingtwisted.

The position (P202 position) to which the nut portion 207 is moved inFIG. 63 indicates a deformed example of the nut portion 207 and it is aposition to which the nut portion 207 is deformed and moved when thefeed screw 205 that has stopped is rotated and accelerated suddenly inthe R202 direction.

In the structure of the conventional rack 208 shown in FIGS. 62 and 63,the rigidity of the plate spring 214 is insufficient such way to copewith the force applied from the thread groove 215 to the nut portion207. The nut portion 207 is thus twisted significantly when the rotationof the feed screw 205 is accelerated/decelerated suddenly, so that theteeth 223 are not fit in the thread groove 215 properly. Furthermore, aproblem that the teeth 223 are disengaged completely from the threadgroove 215 arises.

Furthermore, since the pick-up base 203 is slidable in the radialdirection of the disk 201 with a weak force, a gap is formed between thepick-up base 203 and the first guide shaft 209 of the guiding mechanism211 and between the pick-up base 203 and the second guide shaft 210respectively. The direction of the force applied to the nut portion 207from the thread groove 215 has 3 directional components orthogonal toeach other as explained above. In addition, since the center of thegravity of the pick-up 202 is not the same position where a force isapplied to the nut portion 207, a problem that the pick-up base 203 isvibrated due to the gap of the guiding mechanism 211 arises if the headbase 203 is slid at a sudden acceleration/deceleration.

In such the conventional general disk apparatus, a problem that the rack208 mentioned above is disengaged from the feed screw 205 when in a highspeed accessing, as well as a problem that the pick-up base 203 isvibrated arise respectively. In order to solve those problems, therehave been proposed some countermeasures.

Next, some of the representative countermeasures for those problems willbe explained.

FIG. 64 is a perspective view of the conventional disk apparatus in thesecond example for solving the above-mentioned problem that the rack isdisengaged from the feed screw. This second example is disclosed, forexample, in an unexamined Published Japanese Patent Application,publication No. 5-31479. In this prior art, the same configuration itemsas those of the disk apparatus in the first example shown in FIG. 62 andFIG. 63 will be given the same numerals, omitting redundant explanation.Hereunder, only the differences from the first example will beexplained.

As shown in FIG. 64, at both ends of the feed screw 205 provided,withthe thread groove 215 is formed a ring-like groove 216. The nut portion207 a of the rack 208 is engaged helically with the thread groove of thefeed screw 205. Thus, even when a force is applied to the rack 208 afrom the thread groove 215 of the feed screw 205, the rack 208 a isneither deformed nor disengaged from the feed screw 205. Since aring-like groove 216 is formed at both ends of the feed screw 205respectively, when the nut portion 207 a reaches the ring-like groove216, the nut portion 207 a is disengaged from the feed screw 205.Consequently, the nut portion 207 a can be prevented from being caughtin the thread groove 215. In such a structure, however, the frictionalload in the helically engaged portion between the nut portion 207 a andthe feed screw 205 may be increased by variations of machining accuracyand temperature changes. In such a case, the disk apparatus in thesecond example will arise a problem that the disk cannot be accessedstably.

FIG. 65 is a perspective view of the conventional disk apparatus in thethird example for solving the problem that the rack is disengaged fromthe feed screw. This third example is disclosed, for example, in anunexamined Published Japanese Patent Application, publication No.5-325439. In this prior art, the same configuration items as those ofthe conventional disk apparatus in the first and second example shown inFIGS. 62 to 64 will be given the same numerals, avoiding redundantexplanation. Hereunder, therefore, only the differences from the firstand second examples will be explained.

In FIG. 65, the disk apparatus in the third example is provided with astopper 217 and this stopper 217 is used to limit the movement of thenut portion 207 in the direction for disengaging the nut portion 207from the feed screw 205. Since this stopper 217 is provided, the nutportion 207 can be prevented from being disengaged completely from thethread groove 215 even when the feed screw 205 is rotated at a suddenacceleration/deceleration and the nut portion 207 is deformed in thedirection for disengaging the nut portion 207 from the thread groove215. As a result, it is possible for the disk apparatus in the thirdexample to obtain an effect of solving the above-mentioned problem.

However, since the nut portion 207 is deformed by a force received fromthe thread groove 215 within its movable rage, the force applied to thepick-up base 203 is changed by the deformation of the nut portion 207.And, since the force applied to the pick-up base 203 is changed suchway, the pick-up 203 is vibrated. Thus, the problem that the pick-upbase is vibrated cannot be solved yet here.

FIG. 66 is a perspective view of the conventional disk apparatus in thefourth example for solving the above-mentioned problem that the pick-upbase is vibrated. This fourth example is disclosed, for example, in anunexamined Published Japanese Patent Application, PublicationNo.8-279257. In this prior art, the same configuration items as those ofthe disk apparatus shown in FIG. 62 to FIG. 65 will be given the samenumerals, avoiding redundant explanation. Hereunder, therefore, only thedifferences from the first to third example will be explained.

In FIG. 66, the pick-up base 203 is provided with a guide hole 212 andthe first guide shaft 209 is inserted in this guide hole 212.Consequently, the pick-up 202, guided by the first guide shaft 209, canmove in the radial direction of the disk 201. The pick-up base 203 isprovided with a guide bearing 216 via a bearing spring 219. In the holeof this guide bearing 218 is inserted the second guide shaft 210. Therotational motion of the pick-up base 203 around the first guide shaftis thus limited. The bearing spring 219 is pressing the guide bearing218 against the recording face of the disk 201 in the directionorthogonal to the radial direction of the disk. The guide bearing 218 ispressed against the second guide shaft 210 by this bearing spring 219,so that the vibration of the pick-up base 203 is reduced significantlywhen the disk is accessed fast. However, it is only in the directionhorizontal to the recording face of the disk 201 and vertical to themoving direction of the pick-up base 203 that the bearing spring 219 cansuppress the vibration. Consequently, the bearing spring 219 can obtaina less effect for the vibration of the pick-up base 203 in the directionvertical to the recording face of the disk 201. Because of such theconfiguration of the conventional disk apparatus, the pressing force ofthe bearing spring 219 must further be increased to suppress thevibration of the pick-up base 203. And, when the pressing force of thebearing spring 219 is increased such way, the frictional load betweenthe second guide shaft 210 and the guide bearing 218 is also increased.The traverse motor 204 must thus be formed so as to output a largertorque.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method forcontrolling stepping motors, which can reduce the off-track value infeeding the pick-up of a disk apparatus to reduce the displacement ofthe lens, as well as to reduce the power consumption of the steppingmotor when the stepping motor is driven by dividing the basic step angleinto n angles (n: an integer of 2 or over), and provide a disk apparatusthat uses such the stepping motor controlling method.

Another object of the present invention is to provide a method forcontrolling stepping motors, which can prevent the pick-up of a diskapparatus from moving suddenly in the radial direction of the disk whilethe focus servo or the tracking servo is working and obtain a stableservo operation, as well as a disk apparatus that uses such the steppingmotor controlling method. According to the present invention, errors canbe prevented when in recording and playing back data on and from thedisk apparatus. In addition, the present invention enables the steppingmotor to be formed so that the state of excitation is synchronizedbetween the stepping motor driving means and the stepping motor when itis unknown where the stator of the stepping motor is at rest after thestepping motor is powered or steps out. Furthermore, the stepping motoris formed so that the state of excitation can be synchronized such wayin the stepping motor before the focus servo or tracking servo of thedisk apparatus is turned on.

Another object of the present invention is to provide an opticalinformation recording and playing-back apparatus that can suppress thevibration and heat generation of the stepping motor and move the pick-upfast by controlling the torque generated in the stepping motoreffectively when rotating the stepping motor fast continuously.Furthermore, the optical information recording and playing-backapparatus of the present invention can move the pick-up fast and stablyeven when the stepping motor is driven by dividing the basic step angleinto n angles (n: an integer of 2 or over) to improve the positioningperformance.

In the case of the configuration of the conventional disk apparatus, itis difficult to prevent the nut portion of the rack from beingdisengaged from the thread groove of the feed screw and furthermore itis difficult to suppress the vibration of the pick-up when the pick-upis accelerated/decelerated suddenly. Even when those problems areprevented, the frictional load for sliding the pick-up base in theguiding mechanism is increased and this makes it difficult to access thetarget track on the disk fast and stably.

Another object of the present invention is to provide a disk apparatusthat can prevent the rack from being disengaged from the thread grooveand suppress the vibration of the pick-up in fast traverse operations toenable fast and stable traverse operations.

Another object of the present invention is to avoid generation ofuseless states when changing over the rotation of the stepping motorfrom slow to fast so that the accelerating time for fast rotation of thestepping motor is made shorter than the conventional stepping motorcontrolling method.

The method of the present invention for controlling stepping motorsdivides the basic step angle of the stepping motor into n angles (n: aninteger of 2 or over) to drive the stepping motor, and when the steppingmotor is rotated, it enables the driving current of the stepping motorto be changed at a fixed inclination in proportion to the time.

In the case of the stepping controlling method of the present invention,when it is unknown where the rotator of the stepping motor is at rest,for example, just after the disk apparatus is powered or the steppingmotor steps out, the stepping motor driving current pattern is changedby 1/4 cycle or over so that the state of excitation is synchronizedbetween the stepping motor driving means and the stepping motor.

The disk apparatus of the present invention is formed so that when it isunknown where the rotator of the stepping motor is at rest just afterthe disk apparatus is powered or when the stepping motor steps out, thefocus servo means or the tracking servo means is turned on after thestate of excitation is synchronized between the stepping motor drivingmeans and the stepping motor.

The disk apparatus of the present invention comprises a means ofchanging the pulse rate of the stepping motor driving pulses; a means ofmeasuring the acceleration of the pulse rate; and a means of changingthe amplitude of the stepping motor driving voltage according to thepulse rate and the change rate of the pulse rate. The disk apparatus ofthe preset invention also includes a means of changing the change rateof the voltage applied to the coils of the stepping motor according tothe pulse rate and the change rate of the pulse rate. Furthermore, thedisk apparatus of the present invention includes a means of detectingthe tracking speed of the lens provided above the pick-up according tothe tracking error signal and a means of changing the amplitude of thestepping motor driving voltage according to the values of the detectedvibrations of the lens and the pick-up, obtained by comparing thedetected tracking speed of the lens with the pulse rate, which is aspeed command for the stepping motor.

The disk apparatus of the present invention comprises a head forreading/writing signals from/on a disk; a pick-up base provided with thehead; a traverse motor for moving the head in the radial direction ofthe disk; a feed screw rotated by the traverse motor and provided with athread groove on its outer periphery; a rack provided with a fixingportion fixed to the pick-up base and a nut portion engaged with thethread groove; and a guiding mechanism for guiding the pick-up basemovably in the radial direction of the disk, wherein the fixing portionof the rack is connected to the nut portion by an open-ended parallelspring displaceable in the radial direction of the feed screw.

According to the present invention, therefore, even when the head isaccelerated/decelerated suddenly, the nut portion of the rack can beprevented from being disengaged from the feed screw, so that the head ismoved fast.

The stepping motor controlling method of the present invention comprisesa means of generating the first driving signal for rotating the steppingmotor slowly; a means of generating the second driving signal forrotating the stepping motor fast; and a means of controlling switchingof signals between the first driving signal and the second drivingsignal, wherein the controlling means decides whether or not the rotatorof the stepping motor is positioned near a mechanical stability point Xof the stepping motor according to the voltage of the driving signaloutput from the first driving signal generating means or the statusnumber owned by the first driving signal generating means when therotation of the stepping motor is changed from slow to fast, and whenthe rotator of the stepping motor is positioned near a mechanicalstability point X of the stepping motor, the controlling means outputs acommand to the second driving signal generating means so that the seconddriving signal generating means outputs a driving signal for rotatingthe stepping motor to the next mechanical stability point Y of theabove-mentioned mechanical stability point X in the rotation directionof the stepping motor, then the controlling means switches the signalgenerating means from the first driving signal generating means to thesecond driving signal generating means.

And accordingly, the driving signal, when switching the rotation of thestepping motor to fast using the stepping motor controlling method ofthe present invention, can move the rotator of the stepping motor to amechanical stability point one more ahead than the conventionalcontrolling method will do within the same time.

While the novel features of the invention are set forth particularly inthe appended claims, the invention, both as to organization and content,will be better understood and appreciated, along with other objects andfeatures thereof, from the following detailed description taken inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration of a disk apparatus in the first embodiment ofthe present invention.

FIG. 2 is a wave form chart indicating a stepping motor driving currentin the first embodiment of the present invention.

FIG. 3 is a wave form chart indicating a stepping motor driving currentin the second embodiment of the present invention.

FIG. 4 is a wave form chart indicating a stepping motor driving currentin the third embodiment of the present invention.

FIG. 5 is a block diagram for a configuration of the disk apparatus inthe fifth embodiment of the present invention.

FIG. 6 is a configuration of a stepping motor.

FIG. 7 is an illustration of the driving current pattern 1 of a steppingmotor driving means.

FIG. 8 is an illustration of the driving current pattern 2 of thestepping motor driving means.

FIG. 9 is a configuration of the disk apparatus in the seventh andeighth embodiments of the present invention.

FIG. 10 is a block diagram for a configuration of the disk apparatus inthe ninth embodiment of the present invention.

FIG. 11 is a wave form chart (a) indicating a stepping motor drivingpulse rate in the ninth embodiment of the present invention, a wave formchart (b) indicating a torque generated in the stepping motor in theninth embodiment, and a wave form chart (c) indicating a stepping motordriving voltage in the ninth embodiment.

FIG. 12 is a block diagram for a configuration of the disk apparatus inthe tenth embodiment of the present invention.

FIG. 13 is a wave form chart indicating the voltages flowing in coils ofthe stepping motor in the tenth embodiment of the present invention.

FIG. 14 is a block diagram for a configuration of the disk apparatus inthe eleventh embodiment of the present invention.

FIG. 15 is a block diagram of the disk apparatus in the twelfthembodiment of the present invention.

FIG. 16 is a wave form chart (a) when the stepping motor is rotatedforward continuously starting at the basic step angle, and a wave formchart (b) when the stepping motor is rotated forward continuouslystarting at a mechanical instability point outside the range of thebasic step angle.

FIG. 17 is a wave form chart (a) when the stepping motor is rotatedforward continuously to the basic step angle, a wave form chart (b) whenthe stepping motor is rotated forward continuously to a mechanicalinstability point outside the range of the basic step angle.

FIG. 18 is a perspective view of the disk apparatus in the fourteenthembodiment of the present invention.

FIG. 19 is an expanded side view (a) of a feed screw and a rack in thefourteenth embodiment of the present invention, and expanded top views(b) of the feed screw and the rack in the fourteenth embodiment.

FIG. 20 is perspective views of the feed screw and the rack in thesixteenth embodiment of the present invention.

FIG. 21 is perspective views of the feed screw and the rack in thesixteenth embodiment of the present invention.

FIG. 22 is perspective views of the feed screw and the rack in theseventeenth embodiment of the present invention.

FIG. 23 is perspective views of the feed screw and the rack in theeighteenth embodiment of the present invention.

FIG. 24 is an illustration of the dimensional relationship between anopen-ended parallel spring of the rack and a nut portion in thenineteenth embodiment of the present invention.

FIG. 25 is a perspective view of the disk apparatus in the twentiethembodiment of the present invention.

FIG. 26 is a cross sectional side view of the contact status between apick-up base and a guiding mechanism in the twentieth embodiment of thepresent invention.

FIG. 27 is a side view of the contact status between the pick-up baseand the guiding mechanism in the twentieth embodiment of the presentinvention.

FIG. 28 is a perspective view of the disk apparatus in the twentiethembodiment of the present invention.

FIG. 29 is a configuration of a general stepping motor.

FIG. 30 is a wave form chart for the conventional driving signal pattern1 (for fast rotation).

FIG. 31 is a wave form chart for the conventional driving signal pattern2 (for slow rotation).

FIG. 32 is a wave form chart for the conventional driving signal pattern3 (for slow rotation).

FIG. 33 is a wave form chart for the conventional driving signalchange-over pattern 1.

FIG. 34 is a wave form chart for the conventional driving signalchange-over pattern 2.

FIG. 35 is a characteristic chart for the relationship between theposition and the torque of the stepping motor.

FIG. 36 is a stepping motor control circuit diagram in the twenty-thirdembodiment.

FIG. 37 is a wave form chart for a driving signal change-over pattern inthe twenty-third embodiment of the present invention.

FIG. 38 is a wave form chart for the driving signal change-over patternin the twenty-fourth embodiment of the present invention.

FIG. 39 is a block diagram for a configuration of a conventional diskapparatus.

FIG. 40 is a wave form chart indicating a driving pulse rate of aconventional stepping motor.

FIG. 41 is a block diagram for a configuration of the disk apparatus inthe twenty-fifth embodiment of the present invention.

FIG. 42 is a wave form chart indicating a driving pulse rate of thestepping motor in the twenty-fifth embodiment of the present invention.

FIG. 43 is a block diagram for a configuration of the disk apparatus inthe twenty-sixth embodiment of the present invention.

FIG. 44 is a block diagram for a configuration of the disk apparatus inthe twenty-sixth embodiment of the present invention.

FIG. 45 is a wave form chart for the driving pulse rate of the steppingmotor and the current flowing in the stepping motor in thetwenty-seventh embodiment of the present invention.

FIG. 46 is a block diagram for a configuration of the disk apparatus inthe twenty-eighth embodiment of the present invention.

FIG. 47 is a flow chart for the step-out detection in the twenty-eighthembodiment of the present invention.

FIG. 48 is a block diagram for a configuration of the disk apparatus inthe twenty-ninth embodiment of the present invention.

FIG. 49 is a wave form chart for a driving pulse rate of and torquesgenerated in the stepping motor in the twenty-ninth embodiment of thepresent invention.

FIG. 50 is a wave form chart for the driving pulse rate of and thetorques generated in the stepping motor in the twenty-ninth embodimentof the present invention.

FIG. 51 is a block diagram for a configuration of the disk apparatus inthe thirtieth embodiment of the present invention.

FIG. 52 is a flow chart indicating the operation of the disk apparatusin the thirtieth embodiment of the present invention.

FIG. 53 is a wave form chart indicating a driving pulse rate of thestepping motor in the thirtieth embodiment of the present invention.

FIG. 54 is a configuration of the conventional disk apparatus.

FIG. 55 is a configuration of the conventional stepping motor.

FIG. 56 is a wave form chart for a driving current of the conventionalstepping motor.

FIG. 57 is a block diagram for a configuration of a conventional opticalinformation recording and playing-back apparatus.

FIG. 58 is a wave form chart (a) indicating a driving pulse rate of theconventional stepping motor, is a wave form chart (b) indicating atorque generated in the conventional stepping motor.

FIG. 59 is a configuration of a stepping motor.

FIG. 60 is a wave form chart indicating a voltage flowing in the coilsof a conventional 1-2-phase excitation type stepping motor.

FIG. 61 is a wave form chart indicating a voltage flowing in the coilsof the conventional stepping motor and a rotation angle displacement ofthe stepping motor.

FIG. 62 is a perspective view of the conventional disk apparatus in thefirst embodiment.

FIG. 63 is expanded side views (a) of a feed screw and a rack of theconventional disk apparatus in the first embodiment, expanded top views(b) of the feed screw and the rack in the conventional disk apparatus inthe first embodiment.

FIG. 64 is a perspective view of the conventional disk apparatus in thesecond embodiment.

FIG. 65 is a perspective view of the conventional disk apparatus in thethird embodiment.

FIG. 66 is a perspective view of the conventional disk apparatus in thefourth embodiment.

It will be recognized that some or all of the Figures are schematicrepresentations for purposes of illustration and do not necessarilydepict the actual relative sizes or locations of the elements shown.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder, some embodiments of a stepping motor control method and adisk apparatus of the present invention will be explained with referenceto the attached drawings.

<<First Embodiment>>

FIG. 1 is a block diagram for a configuration of a disk apparatus in thefirst embodiment of the present invention. In the disk apparatus shownin the first embodiment of the present invention, all the configurationitems except for the stepping motor controlling means 101 h are the sameas those of the configuration of the conventional disk apparatus shownin FIG. 64. At first, the disk apparatus shown in the first example ofthe present invention will be explained with reference to FIG. 1.

In FIG. 1, a lens 101 b is provided above a pick-up 101 a, and this lens101 b is held by two springs 101 c and 101 d. The rotational motion ofthe stepping motor 101 f is transmitted to the pick-up 101 a via a feedscrew 101 e. The pick-up 101 a makes a linear movement in the radialdirection of a disk 101 j due to the screw motion of the feed screw 101e. The disk 101 j stores information on its helically-formed tracks. Therotation speed of the disk 101 j is controlled by a spindle motor 1011.Error signals from the pick-up 101 a are transmitted to a servo means101 g. The servo means 101 g transmits output signals for controllingthe springs 101 c and 101 d to the pick-up 101 a so that each errorsignal is cleared to 0. A system controller 101 i is connected to theservo means 101 g, the interface means 101 k, and the spindle motor1011. The system controller 101 i transmits driving command signals formoving the pick-up 101 a to the stepping motor controlling means 101 h.The stepping motor controlling means 101 h controls the stepping motor101 f according to the commands received from the system controller 101i.

When in recording/playing back information on/from the disk apparatus inthe first embodiment, the lens 101 b begins its displacement graduallyin the radial direction of the disk 101 j as it keeps following up thehelically-formed tracks on the disk 101 j. The displacement distance ofthe lens 101 b is detected by the servo means 101 g, and the systemcontroller 101 i, when deciding that the lens 101 b has exceeded aspecified displacement distance, transmits a driving command signal tothe stepping motor controlling means 101 h. Receiving this drivingcommand signal, the stepping motor controlling means 101 h makes thestepping motor 101 f rotate step by step minutely to move the pick-up101 a in the radial direction of the disk 101 j so as to control thedisplacement distance of the lens minutely.

FIG. 2 is a wave form chart indicating a driving current of the steppingmotor in the first embodiment of the present invention. In FIG. 2, awave form 102 a is a driving current wave form representing the flowrate and direction of the current applied to an A-phase coil of thestepping motor on the time axis. A wave form 102 b is a driving currentwave form representing the flow rate and direction of the currentapplied to a B-phase coil of the stepping motor on the time axis. In thewave forms 102 a and 102 b, the forward current flow is represented by apositive value and the reverse current flow is represented by a negativevalue. The driving current wave form, when the stepping motor is rotatedforward, changes from left to right as in FIG. 2. When the steppingmotor is rotated in the reverse direction, the driving current wave formchanges from right to left in FIG. 2.

Hereunder, the operation of the stepping motor driven with the steppingmotor driving current represented as shown above will be explained withreference to FIG. 2 and FIG. 55.

In FIG. 2, when the state of the stepping motor driving current changesfrom 102X to 102Y, the B-phase driving current 102 b is changedgradually at an inclination K in proportional to the time and reachesthe current volume of the state Y. While the stepping motor is rotated,the driving current is changed gradually at an inclination K inproportion to the time, not to be changed in a moment in right anglesteps. This is why the change of the start-up torque generated in thestepping motor can be suppressed within a low value. Unlike conventionalstepping motors, no large and abrupt start-up torque is generated in thestepping motor at this time, so the position of the point P on therotator 106 c of the stepping motor shown in FIG. 55 is changed smoothlyfrom 106X to 106Y.

As shown in the first embodiment of the present invention, because thedriving current of the stepping motor is changed from thebefore-rotation state to the after-rotation state at an inclination K inproportion to the time, the change of the start-up torque to begenerated in the stepping motor can be suppressed low.

When the driving current of the stepping motor is changed at aninclination K in proportion to the time, a large inclination K is takenfor the driving current up to the current volume with which the steppingmotor begins rotating actually and a small inclination K is taken whenthe stepping motor begins rotation. Consequently, the acceleration ofthe stepping motor at the start-up time can further be suppressed low.

Hereunder, explanation will be made for a disk apparatus for which thestepping motor controlling method in the above-mentioned firstembodiment is used.

When using the stepping motor controlling method in the above-mentionedfirst embodiment for the stepping motor controlling means 101 h of thedisk apparatus of the present invention shown in FIG. 1, preferably, theinclination K of the driving current shown in FIG. 2 should be variable.In FIG. 1, an analog circuit is used to create the stepping motorcontrolling means 101 h in the first embodiment. In order to reduce themanufacturing cost, however, a digital circuit or such a digital meansas microcomputer software or LSI-incorporated firmware may be used tocreate the stepping motor controlling means.

When a digital means is used, the wave form of the stepping motordriving current is changed in steps on the resolution level due toquantization. However, it is possible even for a digital means to obtainthe same effect as that of the present invention unless otherwise theresolution is so rough to accelerate the stepping motor rapidly. Inaddition, a command signal for changing the inclination K of the drivingcurrent is also applied to the system controller 101 i.

Hereunder, explanation will be made for a case in which the recordingspeed or the playback speed of the disk is increased in a multiple of M(M: an integer of 2 or above) in the above-mentioned configuration. Whenthe rotation speed of the disk is increased in a multiple of M, the lensfollowing up the track of the disk when in recording or playing back isalso displaced in the radial direction of the disk at a speed in amultiple of M. If the inclination K of the stepping motor drivingcurrent is fixed with respect to such a rotation speed of the disk, thepick-up feed speed becomes slower than the displacement speed of thelens, so the pick-up may not be able to follow up the displacement speedof the lens. The feed speed of the pick-up is proportional to theinclination K of the stepping motor driving current. When theinclination K of the stepping motor driving current is variable,therefore, the system controller 101 i changes the inclination K of thepulse counting means 310 according to the rotation speed of the disk, sothat the pick-up can follow up the displacement speed of the lens.

In the above-mentioned first embodiment of the present invention, inwhich the basic step angle of the stepping motor is divided into nangles (n: an integer of 2 or above) to control the stepping motor, thedriving current of the stepping motor is changed at an inclination K inproportion to the time between the before-rotation state and theafter-rotation state. Consequently, the acceleration of the steppingmotor at the start-up time can be controlled low.

When the stepping motor controlling method in the first embodiment isused for feeding the pick-up of a disk, no acceleration is applied somuch for the pick-up fed by a stepping motor. Thus, the lens shakes lessand the off-track frequency can be reduced significantly. Furthermore,when the inclination K of the pulse counting means 310 is variable, theinclination K can be changed according to the rotation speed of the diskso that the pick-up follows up the displacement speed of the lens.

<<Second Embodiment>>

Hereunder, the second embodiment of the present invention will beexplained with reference to the attached drawings. FIG. 3 is a wave formchart indicating the driving current of the stepping motor in the secondembodiment of the present invention. In FIG. 3, the wave form 103 a is adriving current wave form representing the flow rate and direction ofthe current applied to the A-phase coil of the stepping motor on thetime axis. A wave form 103 b is a driving current wave form representingthe flow rate and direction of the current applied to the B-phase coilof the stepping motor on the time axis. In the wave forms 103 a and 103b, the forward flowing current is represented by a positive value andthe reverse flowing current is represented by a negative value. In FIG.3, the arrow 103F indicates a wave form to appear when the steppingmotor is rotated forward, and the driving current wave form is changedfrom left to right in FIG. 3. The arrow 103R indicates the current waveform to appear when the stepping motor is rotated reversely, and thedriving current wave form is changed from right to left in FIG. 3.

Hereunder, the operation of the stepping motor with a pulse countingmeans 310 as represented above will be explained with reference to FIGS.3 and 55. In FIG. 3, when the stepping motor is rotated forward, thedriving current state is changed from 103X to 103Y, then the B-phasedriving current 103 b is changed gradually in proportion to the time andreaches the current volume in the state 103Y in accordance with thedriving current shown with an arrow 103F. As shown in FIG. 3, thedriving current is not changed in steps in a moment when the steppingmotor in the second embodiment is rotated, but the driving current ischanged gradually in proportion to the time, just like in theaforementioned first embodiment. With this, the start-up torque to begenerated in the stepping motor used in the disk in the secondembodiment can be suppressed low.

If the frictional load applied to the stepping motor is large withrespect of the stepping motor start-up torque, however, the position ofthe point P of the rotator 106 c gives in to the frictional load andstops before it reaches the position 106Y. Thus, it becomes impossibleto control the rotational angle of the stepping motor accurately in FIG.55. To avoid this problem, therefore, in FIG. 3, the B-phase drivingcurrent is flown by a current volume α in the positive direction morethan the current in the first embodiment just like the current wave formshown with an arrow 103F. The rotational angle of the stepping motor inthe second embodiment can thus be adjusted. And, when the current volumeα is adjusted, the position P of the rotator 106 c in FIG. 55 can bestopped at the position 106Y accurately.

When the stepping motor is rotated in the reverse direction, the drivingcurrent state in FIG. 3 is changed from 103Z to 103Y, then the currentvolume reaches the state 103Y in accordance with the driving currentshown with an arrow 103R which is different from the driving currentshown by an arrow 103F for the above-mentioned forward rotation of thestepping motor. The driving current shown with an arrow 103R can adjustthe rotational angle of the stepping motor when the current flowing inthe coil is increased by a current volume α in the negative direction.

Hereunder, explanation will be made for a disk apparatus for which thestepping motor controlling method in the above-mentioned secondembodiment is used.

When the stepping motor controlling method in the second embodiment isused for the stepping motor controlling means 101 h of the diskapparatus in the first embodiment shown in FIG. 1, the disk apparatus inthe second embodiment is formed so as to change the current volume αused for the adjustment shown in FIG. 3. In FIG. 1, the stepping motorcontrolling means 101 h is formed just like the means explained in thefirst embodiment. The system controller 101 i in the second embodimentis formed with additional items so that it can output a command signalfor changing the value of the current volume α.

In the case of the disk apparatus formed in the second embodiment asexplained above, for example, when the type of the stepping motor ischanged and/or when any mechanical specification of the disk apparatusare changed, the relationship between the torque and frictional load ofthe stepping motor may be changed from design values. When the diskapparatus is formed so as to be able to change the current volume α tocope with such specification changes, however, the current volume α canbe adjusted so that the position of the point P on the rotator 106 cshown in FIG. 55 can rest at the position 106Y.

Consequently, in the disk apparatus in the second embodiment, therotation volume of the stepping motor, that is, the feed distance of thepick-up, can be adjusted later so as to be fixed even after anyspecification is changed in the configuration of the disk apparatus.

As shown in the above-mentioned second embodiment of the presentinvention, when the stepping motor is stopped at a mechanicalinstability point outside the range of the basic stepping angle, therotational angle of the stepping motor can be controlled accurately bychanging the direction and volume of the driving current according tothe rotational direction until the mechanical instability point isreached. When this controlling method is used for a disk apparatus, thefeed distance of the pick-up can be adjusted even after anyspecification change in the disk apparatus. In addition, the diskapparatus in the second embodiment can prevent the lens from excessivedisplacement to occur in the pick-up, and accordingly it can alsoprevent the characteristics of the focus servo and the tracking servofrom degradation.

<<Third Embodiment>>

Hereunder, the third embodiment of the present invention will beexplained with reference to FIG. 4.

FIG. 4 is a wave form indicating a driving current of the stepping motorin the third embodiment of the present invention. In FIG. 4, the solidline indicates the wave form of the driving current in the thirdembodiment and the alternative long and short dash line indicates thewave form of the driving current in the first embodiment for comparison.The wave form 104 a is a driving current wave form representing thevolume and direction of the current flowing in the A-phase coil of thestepping motor on the time axis. The wave form 104 b is a drivingcurrent wave form representing the volume and direction of the currentflowing in the B-phase coil of the stepping motor on the time axis. Theforward flowing driving currents (104 a and 104 b) are represented bypositive values and the reverse flowing driving currents (104 s and 104b) are represented by negative values. The current wave form to appearwhen the stepping motor is rotated forward is changed from left to rightin FIG. 4. The current wave form to appear when the stepping motor isrotated reversely is changed from right to left in FIG. 4.

Hereunder, explanation will be made for how the stepping motor rests ata basic step angle position, that is, at a mechanical stability point,due to the driving current of the stepping motor formed as explainedabove in the third embodiment.

In FIG. 4, when the driving current state of the stepping motor ischanged from 104YC to 104ZA, the B-phase driving current 104 b isincreased gradually from 0 to a positive value in proportion to thetime. At this time, the point P of the rotator 106 c shown in FIG. 55 isrotated from the position 106Y to the position 106Z. And, after therotator 106 c reaches the target position 106Z, both A-phase drivingcurrent 104 a and B-phase driving current 104 b are reduced gradually to0 at a rate as shown in the state 104ZA. Then, the A-phase drivingcurrent 104 a and the B-phase driving current 104 b enter the hold state(104ZB) leaving only the current volume β respectively. After this, whenthe stepping motor is rotated forward again, both A-phase and B-phasedriving currents 104 a and 104 b are increased gradually at the samerate as shown in the state 104ZC. After this, the A-phase drivingcurrent 104 a enters the next state.

In the states 104ZA and 104ZC, the rotator rests due to the balance ofthe generated torque between A-phase and B-phase coils of the steppingmotor. Consequently, when the current volume flowing in only one of thecoils is reduced, the balance of the torque between the coils is lostand the rotor begins moving. Thus, the current volumes flowing in bothA-phase and B-phase coils are reduced or increased at the same rate.And, the rotator keeps at rest as is.

Next, explanation will be made for the operation of the rotator forbeing rested at a mechanical instability point outside the range of thebasic step angle with reference to FIGS. 4 and 55.

If, when the stepping motor is rotated forward, the driving currentstate is changed from 104XC to 104YA in FIG. 4, then the B-phase drivingcurrent 104 b is changed gradually from a negative value to 0 inproportion to the time. At this time, the point P of the rotator 106 cshown in FIG. 55 is rotated from the position 106X to the position 106Y.After the rotator stops at the target position 106Y, the A-phase drivingcurrent 104 a is reduced gradually to 0 in proportion to the time asshown in the state 104YA in FIG. 4. Then, the A-phase driving current104 a enters the rest state 104YB leaving only the current volume β.After this, when the rotator is rotated forward again, the A-phasedriving current 104 is increased gradually in proportion to the time asshown in the state 104YC. Then, the B-phase driving current 104 b isincreased with a positive value toward the state 104ZA. In the states104YA and 104YC, the current volumes in both coils are reduced orincreased respectively in proportion to the time, so that the torque ofthe stepping motor is changed gradually with respect to the time.Because no sharp change of torque is applied to the rotator, the rotatorkeeps resting as is due to the frictional force. In the state 104YBshown in FIG. 4, the current volume flowing in the coils of the steppingmotor is left only by β. This is because the position 106Y in FIG. 55 isa mechanical instability point outside the range of the basic step angleof the stepping motor. So, if the current volume flowing in each coil isreduced to 0 completely, the rotator 106 c stops only with themechanical frictional force. If any vibration is applied to the rotatorin this state, the rotator 106 c is shifted to a position 106X or 106Z,which is a mechanical stability point. If such a phenomenon occurs inthe disk apparatus, the pick-up is shifted by vibration, causing thecharacteristics of the focus servo and the tracking servo to bedegraded. To avoid such a trouble, the current volume flowing in eachcoil is not reduced to 0 completely in the third embodiment; only acurrent volume of β is left when the rotator is stopped, so that therotator can rest in a state of vibration free.

Next, explanation will be made for a case in which the stepping motorcontrolling method in the above-mentioned third embodiment is used for adisk apparatus.

When the stepping motor controlling method in the third embodiment isused for the stepping motor controlling means 101 h in the diskapparatus in the first embodiment of the present invention shown in FIG.1, the disk apparatus should preferably be formed so that the currentvolume β used for making the rotator rest as shown in FIG. 4 isvariable. The disk apparatus in the third embodiment 3 is formed so asto use the stepping motor controlling means shown in FIG. 1 and outputcommand signals for changing the current volume β value to the systemcontroller 101 i.

For example, when the type of the stepping motor used for the diskapparatus is changed and/or when any mechanical specification of thedisk apparatus is changed, the relationship between the torque and thefrictional load of the stepping motor may differ from the design ones.The disk apparatus in the third embodiment can cope with suchspecification changes by changing the current volume β, so the currentvolume β can be adjusted after any specification change so that therotator can keeps resting with the necessary minimum current volume.

As shown in FIG. 4, in the states 104XB and 104ZB, the rotator of thestepping motor is positioned at a basic step angle position, that is, atmechanical stability points shown as positions 106X and 106Z in FIG. 55.Thus, the rotator is positioned at a more stable rest point dynamicallythan being positioned at a position 106Y, which is a mechanicalinstability point, and accordingly, it is not easily shifted from theposition. When the disk apparatus is formed so as to change the currentvolume β, therefore, the current volume for keeping the rest state ofthe rotator at positions 106X and 106Z, which are both mechanicalstability points, can be reduced more than the current volume forkeeping the rest state of the rotator at the position 106Y, which is amechanical instability point. This is why the power consumption andcalorific value of the stepping motor in the rest state can be furthersuppressed.

In the third embodiment, as explained above, after the rotator reachesthe target position, the current volume flowing in each coil of thestepping motor is reduced gradually in proportion to the time withoutmoving the rotator and only the residual current volume β is used tokeep the rotator at rest. As a result, the power consumption of thestepping motor in the rest state can be reduced significantly,preventing heat generation of the stepping motor in the thirdembodiment.

Furthermore, because the current volume β can be changed in the steppingmotor controlling method in the third embodiment, the stepping motor canbe kept at rest with the necessary minimum power consumption even afterany mechanical specification of the disk apparatus is changed.

Furthermore, according to whether the rest point of the stepping motoris at a mechanical stability point or at an instability point, thestepping motor can be kept at rest at each stop point with the necessaryminimum power consumption in the stepping motor controlling method inthe third embodiment.

<<Fourth Embodiment>>

Hereunder, the fourth embodiment of the present invention will beexplained with reference to the attached drawings.

In the disk apparatus shown in FIG. 1, if vibration is generated insideor outside the disk apparatus, the lens 101 b is shaken and an errorsignal is transmitted to the servo means 101 g. The error signalindicates a larger amplitude than that of normal operations thatgenerate no vibration. This error signal is a tracking error signal or afocusing error signal. The system controller 101 i, when detecting alarger amplitude error, detects the vibration generated in the diskapparatus. Detecting such vibration, the system controller 101 itransmits a command signal for increasing the current volume of the reststate to the stepping motor controlling means 101 h. The stepping motorcontrolling means 101 h then increases the current volume β more thanthe normal current volume to make the stepping motor rest at the currentposition as explained in FIG. 4 in the third embodiment.

When the vibration stops, a small amplitude error signal is transmittedto the servo means 101 g. Unless the amplitude of the error signal isincreased for a fixed time, the system controller 101 i decides that thevibration is already stopped, then transmits a command signal forreturning the current volume β to the normal one to the stepping motorcontrolling means 101 h. Receiving the command signal, the steppingmotor controlling means 101 h reduces the current volume β to return thecurrent of the resting state to the normal volume.

Since vibration is detected according to the error signal from the servomeans 101 g and the current volume needed for making the stepping motorrest is increased over the normal one such way in the fourth embodiment,the resting position of the stepping motor, that is, the restingposition of the pick-up, can be prevented from being shifted from theresting position, due to vibration. Consequently, the pick-up is nevershifted from its due position even when vibration is generated in thedisk apparatus in the fourth embodiment. Thus, the disk apparatus in thefourth embodiment can be prevented from focus-off and tracking-offerrors. Furthermore, since the current volume is returned to the normalone after vibration stops in the disk apparatus in the fourthembodiment, only the necessary minimum power consumption is needed tokeep the stepping motor at rest while coping with the vibration.

Although an example of recording/playing back information on/from thehelically-formed tracks on a disk is explained in the fourth embodimentof the present invention, the present invention may also be applied fora case of recording/playing back information on/from the concentriccircle tracks of a disk. When recording/playing back information on/fromsuch a concentric circle track, the lens moves to adjacent tracks oneafter another to be displaced above the pick-up. Consequently, thepick-up must also be moved, and the present invention can also apply toa disk being comprised of concentric circle tracks.

Although the driving current of the stepping motor is changed in thefourth embodiment of the present invention, it is also possible toobtain the same effect by changing the voltage between terminals of eachcoil of the stepping motor.

Although explanation is made in the fourth embodiment of the presentinvention for an example of the 1-2 phase excitation in which the basicstep angle of the stepping motor is divided into two angles so that themotor is rotated in units of a 1/2 step angle, it is also possible toobtain the same effect by applying the present invention to a steppingmotor controlling system that divides the basic step angle of thestepping motor further into n angles (n: an integer of 2 or over) sothat the motor is rotated in units of a 1/n step angle.

As explained above, in the stepping motor controlling method thatdivides the basic step angle of the stepping motor into n angles (n: aninteger of 2 or over) to drive the stepping motor, when theabove-mentioned stepping motor is rotated by a 1/n step angle, thedriving current of the stepping motor is changed at an inclination K inproportion to the time between the before-rotation state and theafter-rotation state. Changing the inclination K such way makes itpossible to suppress the start-up torque to be generated in the steppingmotor to a small change. When such the stepping motor controlling methodof the present invention is used for feeding the pick-up fed by astepping motor in a disk apparatus, therefore, no large acceleration isapplied to the pick-up. As a result, shaking of the lens can besuppressed low, reducing the off-track frequency significantly.

<<Fifth Embodiment>>

Hereunder, the fifth embodiment of the stepping motor driving method andthe disk apparatus of the present invention will be explained withreference to the attached drawings.

FIG. 5 is a block diagram for a configuration of the disk apparatus inthe fifth embodiment, and in the sixth embodiment of the presentinvention, to be explained later. Hereunder, the fifth embodiment of thepresent invention will be explained first with reference to the attacheddrawings.

In FIG. 5, a lens 401 b is provided above a pick-up 401 a and the lens401 b is held by springs 401 c and 401 d. The rotational motion of thestepping motor 401 f is transmitted to the pick-up 401 a via a feedscrew 401 e. The pick-up 401 a makes a linear motion in the radialdirection of the disk 401 j. The disk 401 j stores information on itshelically-formed or concentric circle-formed tracks, and the rotationspeed of the disk is controlled by a spindle motor 401 k. Error signalsfrom the pick-up 401 a are transmitted to a servo means 401 g, and theservo means 401 g outputs signals for controlling the springs 401 c and401 d to the pick-up 401 a so as to minimize the size of error signals.

The system controller 401 i in the fifth embodiment is connected to theservo means 401 g and the spindle motor 401 k and transmits drivingcommand signals for feeding the pick-up 401 a to the stepping motorcontrolling means 401 h as needed. Receiving the command from the systemcontroller 401 i, the stepping motor controlling means 401 h drives thestepping motor 401 f.

FIG. 6 is a schematic inner configuration of a general stepping motor.

In FIG. 6, an arrow 402 a indicates a current flowing in the A-phasecoil and an arrow 402 b indicates a current flowing in the B-phase coil.The rotator 402 c has a plurality of pairs of magnetic poles N and S.The point P on the rotator begins a rotational motion when the current402 a flowing in the A-phase coil and the current 402 b flowing in theB-phase coil are changed together and stops when the balance between themagnetic force generated from the coils and the frictional load ofrotation is stabilized.

Positions 402W, 402X, 402Y, and 402Z show consecutive excitationstability points of some excitation stability points of the steppingmotor. The number of magnetic pole pairs and the number of excitationstability points vary with types of stepping motors.

FIG. 7 is a wave form chart representing a driving current pattern ofthe stepping motor driving means 401 h. The driving current patternshown in FIG. 7 is driving current pattern of a general stepping motor.Which is a so-called 2-phase excitation type one.

In FIG. 7, the wave form 403A is a driving current wave formrepresenting the volume and direction of the current flowing in theA-phase coil of the stepping motor 401 f on the time axis. The wave form403B is a driving current wave form representing the volume anddirection of the current flowing in the B-phase coil of the steppingmotor 401 f on the time axis. In the A-phase coil driving current waveform 403A and the B-phase coil driving current wave form 403B, thecurrent flowing forward in each coil is represented by a positive valueand the current flowing reversely in each coil is represented by anegative value.

When the current state is 403W in FIG. 7, the point P on the rotator ofthe stepping motor 401 f shown in FIG. 6 is moved to a stability point,which is the position 402W. In the same way, each of the current states403X, 403Y, and 403Z in FIG. 7 correspond to each of the states in whichthe point P is moved to the positions 402X, 402Y,and 402Z in FIG. 6respectively.

Hereunder, explanation will be made for the operations of the diskapparatus and the stepping motor 401 f according to the stepping motordriving current patterns in the above-mentioned configuration withreference to FIGS. 5 to 7.

The stepping motor driving means 401 h in FIG. 5 is provided withneither encoder nor sensor used for detecting the position of thestepping motor 401 f. Thus, for example, just after the main powersupply of a disk apparatus is initialized (turned on immediately afterit is turned off), the controlling means 401 h cannot know the positionat which the stepping motor 401 f stops. In other words, in the initialstatus in which the stepping motor 401 f is not excited yet, it isunknown where the position P on the rotator of the stepping motor stopsin FIG. 6.

In the stepping motor controlling method in the fifth embodiment of thepresent invention, the state of excitation can be synchronized betweenthe stepping motor driving means 401 h and the stepping motor 401 f asshown in FIG. 5 by changing the driving current pattern of the steppingmotor driving means by 1/4 cycle or over even when the state ofexcitation of the stepping motor, that is, the position of the rotatorof the stepping motor, is unknown. Hereunder, this principle will beexplained.

In FIG. 6, it is assumed that the initial position of the point P on therotator of the stepping motor is at any of the positions 402W, 402X,402Y, and 402Z. Now, it is assumed here that the stepping motor drivingmeans 401 h excites the current state 403X in FIG. 7. With respect tothis excitation, when the initial position of the point P on the rotatorof the stepping motor in FIG. 6 is arranged at the positions 402W, 402X,402Y, and 402Z respectively, the result will be as shown below.

If the initial position of the point P on the rotator of the steppingmotor is arranged at the position 402X in FIG. 6, the state ofexcitation is synchronized between the stepping motor driving means 401h and the position of the stepping motor rotator, that is, the steppingmotor from the beginning.

If the initial position of the point P on the rotator of the steppingmotor is arranged at the position at 402W in FIG. 6, the point P on therotator in FIG. 6 is rotated from the position 402W to the position 402Xwhen the stepping motor driving means excites the current state 403X inthe driving current pattern shown in FIG. 7. If the initial position ofthe point P on the rotator of the stepping motor is arranged at theposition 402Y in FIG. 6, the point P on the rotator in FIG. 6 is rotatedfrom the position 402Y to the position 402X when the stepping motordriving means excites the current state 403X in the driving currentpattern shown in FIG. 7. As a result, whether the initial position ofthe point P is arranged at position 402W or at the position 402Y, thestate of excitation is synchronized between the stepping motor drivingmeans 401 h and the position of the stepping motor rotator, that is, thestepping motor.

If the initial position of the point P on the rotator of the steppingmotor is arranged at the position 402 z in FIG. 6, both A-phase andB-phase coils shown in FIG. 6 are excited to the same polaritymagnetically after the current state of excitation by the stepping motordriving means. Thus, the point P on the rotator remains at the sameposition (402Z).

However, it is when the driving current pattern shown in FIG. 7 is inthe current state 403Z that the point P on the rotator stops at theposition 402Z in the normal excitation state. Consequently, when thepoint P on the rotator stops at the position 402Z while the steppingmotor driving means is in the current state 403X, the state ofexcitation is not synchronized between the stepping motor driving meansand the stepping motor.

This is why the current state of the stepping motor driving means ischanged from 403X to 403Y so that both A-phase and B-phase coils shownin FIG. 6 are excited to the reverse polarity magnetically. The point Pon the rotator is thus moved from the position 402Z to the position402Y.

Consequently, the point P on the rotator is moved to the position 402Ywith respect to the current state 403Y, and the state of excitation issynchronized between the stepping motor driving means and the steppingmotor. The change of the current state from 403X to 403Y in FIG. 7 isequal to a change of 1/4 cycle for the driving current pattern of thestepping motor driving means.

When the position of the rotator of the stepping motor 401 f is unknownin FIG. 5 such way, the driving current pattern of the stepping motordriving means 401 h is changed by 1/4 cycle or over, so that the stateof excitation can be synchronized between the stepping motor drivingmeans 401 h and the stepping motor 401 f.

After the state of excitation is synchronized between the stepping motordriving means 401 h and the stepping motor 401 f, the stepping motor 401f can be controlled in an open loop.

In FIG. 7, the driving current pattern of a general 2-phase excitationtype stepping motor is used for simplifying the explanation of the fifthembodiment of the present invention. In addition to such the 2-phaseexcitation system, however, the fifth embodiment may also apply to the1/2-phase excitation system, as well as the sine wave driving system asshown in FIG. 8 or other various types of stepping motor excitationsystems, each of which drives a stepping motor in 1/N steps (N: aninteger of 2 or over) in a stairstep-like driving current pattern thatmodels the sine wave. When the position of the rotator of the steppingmotor is unknown, the state of excitation can be synchronized betweenthe stepping motor driving means and the stepping motor by changing thedriving current pattern of the stepping motor driving means by 1/4 cycleor over.

<<Sixth Embodiment>>

Hereunder, the sixth embodiment of the present invention will beexplained with reference to the attached drawings.

As explained in the aforementioned fifth embodiment, when the positionof the rotator of the stepping motor is unknown, the current state 403Xis excited as the initial excitation, for example, then the point P onthe rotator is rotated from the position 402Y to the position 402X. Thisis possible only when the initial position of the point P on the rotatorof the stepping motor is at the position 402Y in FIG. 6. As a result,the state of excitation is synchronized between the stepping motordriving means and the stepping motor.

When the state of excitation is synchronized between the stepping motordriving means and the stepping motor such way, the rotator of thestepping motor is moved to an excitation stability point, so that thestepping motor will be rotated suddenly sometimes.

If the stepping motor 401 f is rotated suddenly in FIG. 5, the pick-up401 a is also moved suddenly in the radial direction of the disk 401 j.

The lens 401 b of the pick-up 401 a is thus accelerated so much and thelens 401 b is shaken. This causes the laser beam point to go off thetrack on the disk 401 j, resulting in an off-track error. If theoff-track distance is large at this time, data cannot be recordedcorrectly when in recording and when in playback, a data error iscaused.

If the stepping motor 401 j is rotated suddenly in the case shown inFIG. 5, the lens 401 b of the pick-up 401 a is shaken to cause a largedisplacement. The focus servo operation thus becomes unstable and thelaser beam cannot be focused on the data face of the disk, causingrecording/playback of data to be disabled.

In the case of the stepping motor driving method described in the sixthembodiment of the present invention, after the state of excitation issynchronized between the stepping motor driving means and the steppingmotor, a servo operation is started under the control of the steppingmotor.

In the disk apparatus described in the sixth embodiment of the presentinvention shown in FIG. 5, the state of excitation is synchronizedbetween the stepping motor driving means 401 h and the stepping motor401 f before the servo means 401 g begins a focus servo operation or atracking servo operation. Consequently, sudden movement of the pick-up401 a in the radial direction of the disk 401 j can be prevented duringthe focus servo or tracking servo operation. In the disk apparatus inthe sixth embodiment, therefore, the servo operation is stabilized,preventing errors when in recording and playing back of data.

<<Seventh Embodiment>>

FIG. 9 is a block diagram for a configuration of the disk apparatus inthe seventh embodiment of the present invention. The disk apparatus inthe seventh embodiment is the same as that in the above-mentioned fifthembodiment except that it is additionally provided with a stepping motorstep-out detecting means 405 m.

Hereunder, the seventh embodiment of the present invention will beexplained with reference to the attached drawings.

In FIG. 9, a lens 405 b is provided above a pick-up 405 a. The lens 405b is held by springs 405 c and 405 d. The rotational motion of thestepping motor 405 f is transmitted to the pick-up 405 a via a feedscrew 405 e. The pick-up 405 a makes a linear motion according to therotation of the feed screw in the radial direction of the disk 405 j.

The disk 405 j stores information on its helically or concentriccircle-formed tracks and the rotation speed of the disk 405 j iscontrolled by a spindle motor 405 k. Error signals from the pick-up 405a are transmitted to a servo means 405 g. The servo means 405 g outputssignals for controlling the springs 405 c and 405 d to the pick-up 405 aso as to minimize the size of each error signal.

The system controller 405 i in the seventh embodiment is connected tothe servo means 405 g, the spindle motor 405 k, and the step-outdetecting means 405 m respectively. The system controller 405 i alsooutputs driving command signals for feeding the pick-up 405 a to thestepping motor controlling means 405 h as needed. Receiving such acommand, the stepping motor controlling means 405 h drives the steppingmotor.

Hereunder, the operation of the disk apparatus formed such way in theseventh embodiment will be explained with reference to FIGS. 6, 7, and9.

The step-out detecting means 405 m of the stepping motor shown in FIG. 9detects the step-out of the stepping motor 405 j by checking the currentvolume flowing in each coil and the voltage between terminals of eachcoil of the stepping motor 405 f. When the stepping motor 405 j stepsout, the current volume flowing in each coil and the voltage betweenterminals of each coil of the stepping motor 405 j become larger thanthe values of those taken before the step-out occurs. The step-out ofthe stepping motor can thus be detected by comparing the values of thecurrent volume and the voltages of the coils between those taken beforeand after the stepping motor 405 j is in the step-out.

If the step-out detecting means 405 m detects a step-out of the steppingmotor 405 j, the state of excitation may not be synchronized between thestepping motor driving means 405 h and the stepping motor 405 f. Thedisk apparatus shown in FIG. 9 is provided with neither encoder norsensor used for detecting the position of the stepping motor 405 f. Whenthe step-out means 405 m detects a step-out of the stepping motor 405 f,therefore, it is still unknown where the stepping motor 405 f ispositioned.

This is why it is assumed at first that the initial position of thepoint P on the rotator of the stepping motor is arranged at any of thepositions 402W, 402X, 402Y, and 402Z shown in FIG. 6 when a step-out isdetected in the stepping motor 405 f. It is then assumed that thestepping motor driving means has excited the current state 403X in FIG.7. And, if the initial position of the point P on the rotator of thestepping motor shown in FIG. 6 is arranged at the positions 402W, 402X,402Y, and 402Z respectively with respect to this excitation, the resultwill be as shown below.

If the initial position of the point P on the rotator of the steppingmotor shown in FIG. 6 is arranged at the position 402X in FIG. 6, thestate of excitation is synchronized between the stepping motor drivingmeans 405 h and the position of the stepping motor rotator, that is, thestepping motor 405 f, from the beginning in FIG. 9.

If the initial position of the point P on the rotator of the steppingmotor shown in FIG. 6 is arranged at the position 402W or 402Y in FIG.6, the point P on the rotator shown in FIG. 6 is rotated from theposition 402W to the position 402X or from the position 402Y to theposition 402X due to the excitation of the driving current pattern,performed by the stepping motor driving means 405 h in FIG. 7.Consequently, whether the initial position of the point P is arranged atthe position 402W or at the position 402Y, the state of excitation issynchronized between the stepping motor driving means 405 h shown inFIG. 9 and the stepping motor 405 j.

If the initial position of the point P on the rotator of the steppingmotor shown in FIG. 6 is arranged at the position 402Z, both A-phase andB-phase coils shown in FIG. 6 are excited to the same polaritymagnetically due to the excitation of the current state 403X, performedby the stepping motor driving means 405 h. So, the point P on therotator remains at the position 402Z. However, it is only when thedriving current pattern shown in FIG. 7 is in the current state 403Zthat the point P on the rotator stops at the position 402Z normally.While the point P on the rotator stops at the position 402Z with respectto the current state 403X of the stepping motor driving means 405 h, thestate of excitation is not synchronized between the stepping motordriving means 405 h and the stepping motor 405 f.

This is why the state of excitation is changed from 403X to 403Y for thestepping motor driving means 405 h, so that both A-phase and B-phasecoils shown in FIG. 6 are excited to the reverse polarity magneticallyand the point P on the rotator is moved from the position 402Z to theposition 402Y. As a result, the point on the rotator is moved to thepoint 402Y with respect to the current state 403Y, and the state ofexcitation is synchronized between the stepping motor driving means 405h and the stepping motor 405 f. As shown in FIG. 7, the change of thecurrent state of the driving current pattern from 403X to 403Y is equalto a change of 4/1 cycle of the driving current pattern of the steppingmotor driving means 405 h.

While a step-out is detected in the stepping motor 405 f and theposition of the rotator of the stepping motor driving means 405 f isunknown such way, the driving current pattern of the stepping motordriving means 405 h is changed by 1/4 cycle or over. Consequently, thestate of excitation is synchronized between the stepping motor drivingmeans 405 h and the stepping motor 405 f, so that the stepping motor isrestored from the step-out.

<<Eighth Embodiment>>

Hereunder, the disk apparatus in the eighth embodiment of the presentinvention will be explained with reference to the attached drawings. Theconfiguration of the disk apparatus described in the eighth embodimentof the present invention is almost the same as that in theabove-mentioned seventh embodiment shown in FIG. 9 except it isadditionally provided with a stepping motor step-out detecting means 405m. Since the configuration of the disk apparatus shown in FIG. 9 isexplained already in the seventh embodiment, it is not explained here.

When the stepping motor 405 f shown in FIG. 9 steps out, the steppingmotor 405 f cannot follow up accurately, the driving current patternwhich is output from the stepping motor driving means 405 h, for of thestepping motor 405 f. The stepping motor 405 f will thus make anirregular rotational motion and stop suddenly.

At this time, the pick-up 405 a is moved irregularly in the radialdirection of the disk 405 j, so the lens is shaken, causing the focusservo and the tracking servo of the servo means 405 g to go off.

In the case that the focus servo or the tracking servo of the diskapparatus go off, the data recording/playback processing is stopped.Thus, the disk apparatus restarts and stabilize the servo operationimmediately to restart the data recording/playback processing.

As explained in the seventh embodiment, when the stepping motor 405 fsteps out and the position of the rotator of the stepping motor 405 f isunknown, then the current state 403X in FIG. 7 is excited to restore thestepping motor from the step-out and the point P on the rotator in FIG.6 is rotated from the position 402Y to the position 402X due to theexcitation of the current state 403X, performed by the stepping motordriving means 405 h if the point P on the rotator of the stepping motorshown in FIG. 6 is arranged at the position 402Y. As a result, the stateof excitation is synchronized between the stepping motor driving means405 h and the stepping motor 405 f. When the state of excitation issynchronized between the stepping motor driving means 405 h and thestepping motor 405 f, the rotator is moved to an excitation stabilitypoint, then the rotation of the stepping motor 405 f may be startedsuddenly.

If the focus servo and the tracking servo of the disk apparatus go offdue to a step-out of the stepping motor, the servo operation may go offagain after the state of excitation is synchronized between the steppingmotor driving means 405 h and the stepping motor 405 f even when theservo operation is restarted and stabilized immediately. Such a servooperation should thus preferably be avoided. Because, the datarecording/playback processing in the disk apparatus is stopped twice;when the stepping motor steps out and when the stepping motor isrestored from the step-out.

To avoid such the trouble in the eighth embodiment of the presentinvention, if the step-out detecting means 405 m detects a step-out ofthe stepping motor 405 f and the servo operation of the servo means 405g is turned off in the disk apparatus shown in FIG. 9, the servo means405 g does not restart the servo operation immediately, but the state ofexcitation is synchronized between the stepping motor driving means 405h and the stepping motor 405 f before the stepping motor is restoredfrom the step-out. After this, the disk apparatus in the eighthembodiment allows the servo means 405 g to restart the servo operation.

As explained above, in the disk apparatus defined in the eighthembodiment, the stepping motor is restored from the step-out at first,then the servo means restarts the servo operation. So, the pick-up isprevented from sudden movement in the radial direction of the disk afterthe servo operation is restarted.

Consequently, data recording/playback processing in the disk apparatusin the eighth embodiment is stopped only when the stepping motor stepsout, and the recording/playback processing is not stopped when thestepping motor is restored from a step-out. The stop frequency of datarecording/playback processing executed in the eighth embodiment can thusbe reduced to only once.

In the fifth, sixth, seventh, and eighth embodiments explained above, anoptical pick-up used in a disk apparatus is taken as an example of acontrolling object driven by a stepping motor. The present inventiondoes not limit the pick-up only to those in the above-mentionedembodiments. The stepping motor controlling method and the diskapparatus of the present invention are also effective for any diskapparatus whose magnetic head is driven by a stepping motor.

In the fifth to eighth embodiments of the present invention as explainedabove, when it is unknown where the rotator of the stepping motor ispositioned just after the power supply is turned on or the steppingmotor steps out, the driving current pattern of the stepping motordriving means is changed by 1/4 cycle or over to synchronize the stateof excitation between the stepping motor driving means and the steppingmotor.

Furthermore, in the sixth and eighth embodiments, after the state ofexcitation is synchronized between the stepping motor driving means andthe stepping motor, the focus servo means or the tracking servo meansexecutes a servo operation. With the processings executed in the orderas explained above, it is possible to prevent the servo-off to be causedby sudden rotation of the stepping motor due to the synchronization ofthe state of excitation between the stepping motor driving means and thestepping motor during data recording/playback processing in the diskapparatus, so that errors can be prevented when in a recording/playbackprocessing in the disk apparatus.

<<Ninth Embodiment>>

Hereunder, the ninth embodiment of the present invention will beexplained with reference to the attached drawings. The sameconfiguration items as those of the conventional example shown in FIG.57 will be given the same numerals. FIG. 10 is a block diagram of aconfiguration of the disk apparatus in the ninth embodiment of thepresent invention. FIG. 11 is a chart indicating the time relationshipamong the pulse rate, the generation torque, the necessary torque, andthe driving voltage in the ninth embodiment.

In FIG. 10, the disk 301 has a helically-formed information tracks andthe spindle motor 302 is a driving source for rotating the disk 301. Thepick-up 303 is moved by the stepping motor 307 in the radial directionof the disk 301. A lens 304 is provided in the pick-up 303. The focusservo means 305 drives the focus actuator to be explained later so thatthe lens 304 is kept away by a certain distance from the disk 301according to the focus error signal (not illustrated) indicating adisplacement from the disk 301. The focus actuator is comprised of anelectromagnetic circuit (not illustrated) and used to move the lens 304vertically to the recording face of the disk 301.

The tracking servo means 306 drives a tracking actuator to be explainedlater so that the lens 304 follows up a given track on the disk 301according to the tracking error signal for indicating a displacementfrom a track (not illustrated) on the disk 301. The tracking actuator iscomprised of an electromagnetic circuit (not illustrated) and used formoving the lens 304 horizontally on the recording face of the disk 301.

The stepping motor 307 for moving the pick-up 303 is driven andcontrolled by the stepping motor driving means 308. The pick-up positiondetecting means 309 detects the current position of the pick-up 303 fromthe address information included in the data read from the pick-up 303.The pulse counting means 310 counts the number of stepping motor drivingpulses for moving the pick-up 303 from the current position of thepick-up 303 detected by the pick-up position detecting means 309 to atarget address entered from external. The pulse rate pattern creatingmeans 311 creates a pulse rate pattern of the pulses entered to thestepping motor driving means 308 according to the number of pulsescounted by the pulse counting means 310. The pulse rate measuring means313 is comprised of a timer used to measure the pulse rate created bythe pulse rate pattern creating means 311, and other items. The pulserate change rate measuring means 315 is comprised of a timer formeasuring the change rate of the pulse rate created by the pulse ratecreating means 311, and other items. The driving voltage variable means314 changes the driving voltage of the stepping motor driving means 308according to the values measured by the pulse rate measuring means 313and by the pulse rate change rate measuring means 315. The pulse ratepattern variable means 316 changes the pulse rate change rate from thepulse rate pattern creating means 311 according to the values measuredby the pulse rate measuring means 313 and by the pulse rate change ratemeasuring means 315. The feed screw 312 holds the pick-up 303 movably inthe radial direction of the disk 301 and transmits the torque of thestepping motor 307 to the pick-up 303.

Next, the operation of the disk apparatus formed as explained above inthe ninth embodiment of the present invention will be explained.

The lens 304 used to read information from the disk 301 via the pick-up303 is controlled by the electromagnetic actuator so that it can be keptfocused on the disk 301 using the focus servo means 305 and it canfollow up the target track of the disk 301 using the tracking servomeans 306.

In order to access a given track, the current position of the pick-up303 is recognized at first. In order to detect the current position ofthe pick-up 303, address information is read from the disk 301 via thepick-up 303. The pick-up position detecting means 309 then detects thecurrent position of the pick-up 303 from the address information. Thepulse counting means 310 counts the number of pulses necessary formoving from the detected current pick-up position to a target track.

Next, the operation of the tracking servo means 306 is stopped, then thepulse rate pattern creating means 311 being comprised of amicrocomputer, etc. outputs data by changing the pulse rate change rateas shown in (a) of FIG. 11. The driving voltage of the stepping motordriving means 308 is changed as shown in (c) of FIG. 11, so that thestepping motor 307 is driven to move the pick-up 303. After the pick-up303 is moved, the tracking servo means 306 is started again torecord/play back information.

In FIG. 11, (a) indicates a pulse rate, (b) indicates a torque generatedin the stepping motor 307 and a necessary torque for driving thestepping motor 307 at a pulse rate (a). (c) indicates an amplitude ofthe driving voltage. The output of the pulse rate shown in (a) isstarted with a frequency with which the stepping motor 307 can bestarted up.

The frequency (pulse rate) output from the pulse rate pattern creatingmeans 311 and the change rate of the frequency (pulse rate change rate)are measured by the pulse rate measuring means 313 and the pulse ratechange rate measuring means 315 respectively. The results are entered tothe pulse rate pattern variable means 316. The pulse rate patternvariable means 316 is constructed by a microcomputer, etc. and used tostore the relationship between a pulse rate and a pulse rate change ratethat can suppress generation of a surplus torque found beforehand fromthe motor torque characteristics and the mechanical friction load in itsmemory, etc. According to this relationship, the pulse rate change rateof the pulse rate pattern creating means 311 is changed over. As aresult, the pulse rate output means 311 outputs the pulse rate as shownin (a) of FIG. 11. In addition, the results of the pulse rate measuringmeans 313 and the pulse rate change rate measuring means 315 are alsoentered to the driving voltage amplitude variable means 314. The drivingvoltage amplitude variable means 314 is constructed by a microcomputer,a transistor, a resistor, etc. and used to control the voltage amplitudeto be applied to each coil of the stepping motor 307 of the steppingmotor driving means 308 as shown in (c) of FIG. 11.

With the configuration as shown above, the pulse rate change rate ischanged as shown in (a) of FIG. 11, so that the stepping motor 307 canbe accelerated with the maximum torque and the surplus torque issuppressed to suppress vibration. When in decelerating, the drivingvoltage is lowered to minimize the surplus torque of the stepping motoras shown in (c) of FIG. 11. Thus, the optimized driving force istransmitted to the pick-up 303 via the feed screw 31, enabling thepick-up 303 to be moved fast.

<<Tenth Embodiment>>

Hereunder, the tenth embodiment of the present invention will beexplained with reference to the attached drawings. In the tenthembodiment, the same configuration items as the conventional diskapparatus shown in FIG. 57 will be given the same numerals. FIG. 12 is ablock diagram for a configuration of the disk apparatus in the tenthembodiment of the present invention. In this embodiment, only thedifferences from the conventional disk apparatus shown in FIG. 57 willbe explained.

In FIG. 12, the pulse rate measuring means 313 measures the pulse rateof the pulse rate pattern creating means 311. The pulse rate change ratemeasuring means 315 measures the pulse rate change rate of the pulserate pattern creating means 311. The driving voltage change ratevariable means 317 changes the driving voltage change rate of thestepping motor driving mean 308 according to the measured values of thepulse rate measuring means 313 and the pulse rate change rate measuringmeans 315.

FIG. 13 is a wave form chart indicating the voltages applied to theA-phase and B-phase coils of the stepping motor 308 in the tenthembodiment of the present invention on the time axis.

Next, the operation of the disk apparatus formed as explained above inthe tenth embodiment of the present invention will be explained withreference to FIG. 13. Although the driving voltage amplitude of thestepping motor 307 is changed according to the measured values of thepulse rate measuring means 313 and the pulse rate change rate measuringmeans 315 in the above-mentioned ninth embodiment, the driving voltagechange rate (K) of the stepping motor 307 is changed in this tenthembodiment. In addition, the driving voltage of the stepping motor 307is not changed in steps in a moment, but it is changed gradually inproportion to the time by reducing the change rate (K) where thestepping motor 307 is rotated slowly without any torque as shown in FIG.13. Consequently, the change of the start-up torque generated in thestepping motor 307 is suppressed low to suppress the vibration of thestepping motor 307. In addition, when a torque is needed, for example,when the stepping motor is accelerated and the pick-up is moved fast,the change rate of the driving voltage of the stepping motor 307 isincreased to generate a large start-up torque by changing the drivingvoltage in a moment. With this configuration, the disk apparatus in thetenth embodiment can move the pick-up 303 fast and stably.

<<Eleventh Embodiment>>

Hereunder, the eleventh embodiment of the present invention will beexplained with reference to the attached drawings. The sameconfiguration items as those of the conventional example shown in FIG.55 will be given the same numerals. FIG. 14 is a block diagram for aconfiguration of the disk apparatus in the eleventh embodiment of thepresent invention. In this embodiment, only the differences from theconventional apparatus one will be explained.

In FIG. 14, the pulse rate measuring means 313 measures the pulse rateof the pulse rate pattern creating means 311. The tracking speeddetecting means 318 measures the speed with which the lens 304 crossesthe tracks, using a timer, etc. according to the tracking error signalindicating a displacement value from the tracking of the lens 304,output from the pick-up 303. The lens vibration detecting means 319subtracts the output of the pulse rate measuring means 313 from theoutput of the tracking speed detecting means 318 to detect the vibrationvalue of the lens 304 with respect to the pick-up 303. The drivingvoltage variable means 314 changes the driving voltage amplitude of thestepping motor driving means 308 according to the detected value of thelens vibration detecting means 319.

Next, the operation of the disk apparatus formed as explained above inthe eleventh embodiment of the present invention will be explained withreference to FIG. 14.

Although the driving voltage amplitude of the stepping motor 307 ischanged according to the pulse rate and the pulse rate change rate inthe above-mentioned ninth embodiment, the driving voltage amplitude ofthe stepping motor 307 is changed according to the vibration of thelens, detected by the lens vibration detecting means 319 in thiseleventh embodiment. In other words, when driving the stepping motor 307to move the pick-up 303, the pick-up 303 generates vibration almostcorresponding to the torque characteristics and the mechanical loadcharacteristics of the stepping motor. Consequently, the vibration isalso transmitted to the lens 304 in the pick-up 303, so the lens 304 isshaken in the movement together with the pick-up.

Consequently, the tracking speed detecting means 318 subtracts the pulserate (that is, the target speed of the stepping motor 307) detected bythe pulse rate measuring means 313 from the moving speed of the lens 304to obtain the vibration value of the lens 304. When a detected vibrationvalue is positive (track speed>pulse rate), the pick-up 303 is movedforward too much with respect to the pulse rate. In other words, itmeans that the torque is excessive. Consequently, when the drivingvoltage amplitude of the stepping motor 307 is lowered, the torque isreduced and the surplus torque is suppressed. When a detected amplitudevalue is negative (track speed<pulse rate), the pick-up 303 is delayedwith respect to the pulse rate. This means that the torque isinsufficient. In this case, therefore, the torque generation isincreased to prevent shortage of torque. With such a configuration givento the disk apparatus in this eleventh embodiment, the stepping motor307 can generate the optimized torque and transmit a proper drivingforce to the pick-up 303 via the feed screw 312 to move the pick-up 303stably even when the mechanical friction load, etc. are changed.

<<Twelfth Embodiment>>

Hereunder, the twelfth embodiment of the present invention will beexplained with reference to the attached drawings. The sameconfiguration items as those of the conventional example shown in FIG.57 and those of the eleventh embodiment will be given the same numerals.FIG. 15 is a block diagram for a configuration of the disk apparatus inthe twelfth embodiment of the present invention. In this embodiment,only the differences from the eleventh embodiment will be explained.

In the twelfth embodiment shown in FIG. 15, a switching means 320 beingcomprised of a transistor, etc. is provided. In the pick-up 303 isincorporated a tracking actuator (not illustrated). The lens 304 ismoved by the tracking actuator.

To one end of the switching means 320 is connected the input portion ofthe tracking actuator and the other end of the switching means 320 isformed so as to be switched between the output of the tracking servomeans 306 and the output of the lens vibration detecting means 319.

Next, the operation of the disk apparatus formed as explained above inthe twelfth embodiment of the present invention will be explained withreference to FIG. 15. Although the tracking servo means 306 is openedwhen the stepping motor 307 is driven to move the pick-up 303 in theconventional example shown in FIG. 57 and in the twelfth embodiment, themeasured value from the lens vibration detecting means 319 is entered tothe tracking actuator in the twelfth embodiment. When the stepping motor307 is driven to move the pick-up 303, the pick-up 303 generatesvibration corresponding to the torque and mechanical loadcharacteristics of the stepping motor. This vibration is alsotransmitted to the lens 304 in the pick-up 303, so that the lens 304 isshaken in the movement together with the pick-up 303.

Consequently, the vibration value of the lens 304 is obtained bysubtracting the pulse rate detected by the pulse rate measuring means313 (that is, the target speed of the stepping motor 307) from themoving speed of the lens 304, detected by the tracking speed detectingmeans 318. Since the stepping motor 307 is rotated synchronously withthe pulse rate, the pulse rate can be regarded to be equal to the movingspeed of the pick-up 303. Thus, the vibration value detected by the lensvibration detecting means 319 can be taken as a relative speed of thelens 304 with respect to the pick-up 303. The vibration value detectedby the lens vibration detecting means 319 is returned to the trackingactuator in the pick-up 303 using the switching means 320 so that thevibration value becomes 0.

According to such the configuration, the vibration of the lens 304 withrespect to the pick-up 303 can be suppressed even while the pick-up 303is moving. And, the lens 304 is controlled so as to be positioned in thecenter of the movable range of the pick-up 303. The disk apparatus inthe twelfth embodiment can thus suppress the displacement of the lens304 to 0 after the pick-up 303 is moved. So, the error from the targettrack is reduced significantly after the pick-up 303 is moved. As aresult, the disk apparatus in the twelfth embodiment can shorten thetime to move the residual distance and accordingly improve the accessperformance.

<<Thirteenth Embodiment>>

Hereunder, the thirteenth embodiment of the present invention will beexplained with reference to the attached drawings. FIGS. 16 and 17 arewave form charts indicating the voltages applied to the A-phase andB-phase coils of the stepping motor and the torque generated in thestepping motor while the pick-up is moving on the time axisrespectively. In FIGS. 16 and 17, the solid line indicates thethirteenth embodiment and the dotted line indicates the conventionalexample respectively.

(a) of FIG. 16 is a wave form chart when the rotator that has beenstopped in the range of the basic step angle (in FIG. 59, the point P isarranged at the position 310X) is rotated forward. In (a) of FIG. 16,the wave forms 307 a 1, 307 b 1, and 307 c 1 indicate the voltageapplied to the A-phase coil, the voltage applied to the B-phase coil,and the torque generated in the stepping motor respectively. In FIG. 16,it is assumed that a torque is generated so that when the stepping motordriving voltage applied to each of the A-phase and B-phase coils is inthe stepping motor 307X state, the point P shown in FIG. 59 is arrangedat the position 310X. In the same way, when the voltage is in thestepping motor 307Y state, a torque is generated so that the point P isarranged at the position 310Y and when the voltage is in the steppingmotor 307Z state, a torque is generated so that the point P is arrangedat the position 310Z.

(b) of FIG. 16 is a wave form chart indicating a continuous forwardrotation of the rotator after a stop at a mechanical instability pointoutside the range of the basic step angle (in FIG. 59, the point P isarranged at the position 310Y). In (b) of FIG. 16, the wave forms 307 a2, 307 b 2, and 307 c 2 indicate the voltage applied to the A-phasecoil, the voltage applied to the B-phase coil, and the torque generatedin the stepping motor respectively.

(a) of FIG. 17 is a wave form chart indicating forward continuousrotation of the stepping motor so as to be stopped at a basic step angleposition (in FIG. 59, the point is arranged at the position 310). In (a)of FIG. 17, the wave forms 307 a 3, 307 b 3, and 307 c 3 indicate thevoltage applied to the A-phase coil, the voltage applied to the B-phasecoil, and the torque generated in the stepping motor respectively.

(b) of FIG. 17 is a wave form chart indicating continuous forwardrotation of the stepping motor so as to be stopped at a mechanicalinstability point outside the range of the basic step angle (in FIG. 59,the point P is arranged at the position 310Y). In (b) of FIG. 17, thewave forms 307 a 4, 307 b 4, and 307 c 4 indicate the voltage applied tothe A-phase coil, the voltage applied to the B-phase coil, and thetorque generated in the stepping motor respectively.

Next, the operation of the stepping motor will be explained withreference to (a) and (b) of FIG. 16, as well as FIG. 59. The operationis performed just after continuous rotation is started with the steppingmotor driving voltage explained above.

When the stepping motor is rotated to move the rotator forwardcontinuously while the point P stops at position 310X in FIG. 59, theconventional system performs an operation as shown with the dotted linein (a) of FIG. 16.

When a fixed voltage is applied only to the A-phase coil and no voltage(0) is applied to the B-phase coil, the point P on the rotator isrotated to the position 310Y (mechanical instability point). Then, afixed voltage is applied to both A-phase and B-phase coils, so that thepoint P on the rotator is rotated to the position 310Z (basic step angleposition). Hereunder, as shown with the dotted line in (a) of FIG. 16, avoltage is applied sequentially to the A-phase and B-phase coils torotate the stepping motor to move the point P continuously.

When the rotator is driven as explained above, a voltage is applied toeither the A-phase coil or the B-phase coil at a mechanical instabilitypoint and the torque is generated less than when a fixed voltage isapplied to both A-phase and B-phase coils. Thus, the motor is vibratedby the change of generated torque.

On the other hand, in the thirteenth embodiment, when the rotator isrotated forward continuously from a basic step angle position 310X (FIG.59) as shown with a solid line in (a) of FIG. 16(a), the driving voltageis applied to both A-phase and B-phase coils so that the rotator isrotated forward to a basic step angle position 310Z (FIG. 59) next tothe basic step angle position 310X (FIG. 59). After this, since only thedriving voltage applied to basic step angle positions is appliedsequentially to both A-phase and B-phase coils, a fixed voltage is keptapplied to both A-phase and B-phase coils during continuous rotation.Thus, the stepping motor can be driven without any torque change.

When the stepping motor is started to move the rotator forwardcontinuously while the point P stops at the position 310Y (mechanicalinstability position) in FIG. 49, the driving voltage applied to thebasic step angle position 310Z (FIG. 59) closest to the position 310Y(FIG. 59), which is a mechanical instability point in the forwarddirection as shown with a solid line in (b) of FIG. 16, is applied toboth A-phase and B-phase coils. After this, only the driving voltageapplied to basic step angle positions is applied sequentially to bothA-phase and B-phase coils. Consequently, a fixed voltage is kept appliedto both A-phase and B-phase coils during continuous rotation, so thatthe stepping motor can be driven without any torque change.

Next, the operation for ending continuous rotation of the rotator (tostop the stepping motor) will be explained with reference to (a) and (b)of FIG. 17, as well as FIG. 59. While in continuous feeding of therotator, however, only the driving voltage applied to basic step anglepositions is applied to both A-phase and B-phase coils.

When the point P is to be stopped at the position 310Z (a basic stepangle position) while the rotator shown in FIG. 59 is rotated forward,the driving voltage applied to the last basic step angle position 310Xas shown in (a) of FIG. 17 is applied to both A-phase and B-phase coils.As a result, continuous driving of the stepping motor is ended withoutany torque change.

In the case that the point P is to be stopped at the position 310Y (amechanical instability position) when the rotator 310c shown in FIG. 59is rotated forward, the conventional system generates a torque changewhen the rotator is driven to the last mechanical instability position310Y (FIG. 59) as shown with a dotted line in (b) of FIG. 17. In thethirteenth embodiment, however, the driving voltage applied to amechanical instability point outside the range of the basic step angleis applied to the A-phase coil only for driving the rotator to the lastmechanical instability position 310Y (FIG. 59) as shown with a solidline in (b) of FIG. 17 and the driving voltage strength is increased fora fixed time more than the driving voltage applied to basic step anglepositions. The disk apparatus in the thirteenth embodiment can thusprevent torque generation when it stops and improve the accuracy to movethe rotator to a mechanical instability position 310Y.

As explained above, the disk apparatus in the ninth to thirteenthembodiments can move the pick-up in the optimal state by measuring thepulse rate and the pulse rate change rate, then by changing the pulserate change rate and the stepping motor driving voltage according to themeasured values.

In addition, when in acceleration, the disk apparatus drives thestepping motor with the maximum torque and changes the pulse rate changerate to suppress surplus torque generation. Consequently, the diskapparatus in the ninth to thirteenth embodiments allows data on a diskto be accessed fast and stably while vibration is suppressed.

<<Fourteenth Embodiment>>

Hereunder, the fourteenth embodiment of the present invention will beexplained with reference to the attached drawings.

In the fourteenth embodiment, the same configuration items as those ofthe conventional disk apparatus shown in FIGS. 62 to 66 will be giventhe same numerals, omitting redundant explanation. Thus, only thedifferences from the conventional disk apparatus will be explained here.

FIG. 18 is a perspective view of a portion of the disk apparatus nearthe pick-up in the fourteenth embodiment of the present invention. Asshown in FIG. 18, the disk apparatus in the fourteenth embodiment isprovided with an cautilever parallel spring 221 connecting a fixingportion of the rack 208 to a nut 207. FIG. 19 is an expanded side viewand an expanded front view of a portion near the rack 208 and the feedscrew 205 shown in FIG. 18.

In the fourteenth embodiment, the cautilever parallel spring 221connects the fixing portion of the rack 208 to the nut 207.Consequently, the nut 207 is given a high rigidity in both tangent lineand rotary shaft directions of the feed screw 205 at a point where athread groove 215 is in contact with the teeth 223 with respect to theforce applied from the thread groove 215 to the nut 207. In addition, atthe point where the thread groove 215 comes in contact with the teeth223, the nut 207 is moved in parallel to the feed screw while it is fitin the feed screw 205 without being twisted in the radial direction ofthe feed screw 205. The position P201 in (b) of FIG. 19 indicates aposition to which the nut is moved in parallel to the feed screw 205when rotation of the feed screw 205 is started fast suddenly in thedirection of R201.

The nut portion 207 in the fourteenth embodiment is given a highrigidity against twisting such way. The nut portion 207 is thus lessdeformed than the rack 208 in the conventional disk apparatus shown inFIG. 62, so that the teeth 223 are not disengaged from the thread grooveeasily. Furthermore, when the movement of the pick-up base 203 isblocked by anything, it is prevented that the teeth 223 are disengagedfrom the thread groove 215 and the teeth 223 bite into the thread groove215, which will cause the teeth 223 to be damaged. Furthermore, the nutportion 207 is kept fit in the feed screw 215 and moved in parallel tothe feed screw, so the engagement of the thread groove 215 with theteeth 223 is not changed suddenly. The strength and direction of theforce applied from the teeth 223 to the pick-up base 203 is thus notchanged suddenly. In the fourteenth embodiment, therefore, the pick-upbase 203 is not vibrated so much.

The disk apparatus in the fourteenth embodiment can be provided with anelastic member (not illustrated) such as a coil spring between the nutportion 207 and the pick-up base 203, so that the nut portion 207 ispressed against the feed screw 205 forcibly. In this case, since therigidity of the open-sided parallel spring in the radial direction ofthe feed screw 205 is low, even an elastic body with a weak force canpress the nut portion 207 against the feed screw 205. The nut portion207 can thus be fit to the feed screw 215 surely without increasing thefrictional load.

The disk apparatus in the fourteenth embodiment of the present inventioncomprises a pick-up used for reading/writing signals from/on a disk; apick-up base on which the pick-up is mounted; a traverse motor formoving the pick-up in the radial direction of the disk; a feed screwrotated by the traverse motor and provided with a thread groove on itsouter periphery; a rack having a fitting portion fixed to the pick-upbase and a nut portion fit in the thread groove; and a guiding mechanismfor guiding the pick-up base movably in the radial direction of thedisk. And, in this disk apparatus, the fixing portion of the rack isconnected to the nut portion by the open-sided parallel springdisplaceable in the radial direction of the feed screw.

Consequently, according to the disk apparatus in the fourteenthembodiment, the nut portion of the rack can be prevented from beingreleased from the screw even when the pick-up is accelerated anddecelerated suddenly. The pick-up can thus be moved fast.

<<Fifteenth Embodiment>>

FIG. 20 is a perspective view of the rack 208 of the disk apparatus inthe fifteenth embodiment of the present invention. The cantileverparallel spring 221 connects the fixing portion 206 of the rack 208 tothe nut portion 207. In the disk apparatus in the fifteenth embodiment,the free end of the open-sided parallel spring 221 is extended in thedirection of the rotary shaft of the feed screw 205. With such aconfiguration, the sliding direction (shown by the arrow A in FIG. 20)of the pick-up base 203 is aligned to the buckling direction (shown bythe arrow B in FIG. 20) of the cantilever parallel spring 221.Generally, the buckling direction of a plate has a high rigidity, so therigidity of the rack 208 can be improved in the sliding direction of thepick-up base 203. The nut portion 207 can thus be prevented from beingdeformed more effectively when the feed screw 215 is accelerated anddecelerated suddenly.

In the disk apparatus in the fifteenth embodiment of the presentinvention, the free end of the open-sided parallel spring provided inthe rack is extended in the direction of the rotary shaft of the feedscrew.

According to the disk apparatus in the fifteenth embodiment, therefore,the sliding direction of the pick-up is aligned to the bucklingdirection of the plate spring. Since the plate spring has a highrigidity in the buckling direction, the rack can also secure a highrigidity in the sliding direction of the pick-up. The pick-up can thusbe moved fast.

<<Sixteenth Embodiment>>

FIG. 21 is a perspective view of a rack 208 of the disk apparatus in thesixteenth embodiment of the present invention. In the disk apparatus inthe sixteenth embodiment, a stopper 212 is provided to limit the movingdistance of the nut portion 207 in the movable direction. In FIG. 19,the nut portion 207 is moved to the position shown with an alternatelong and short dash line (position P201) when in sliding. The movingdirection of the nut portion 207 is limited only in the verticaldirection to the rotary shaft of the feed screw 215 when in suddenacceleration and deceleration. Thus, the stopper 212 does not need alarge area for holding the rear of the nut portion 207, so that thestopper 212 can prevent the nut portion 207 from going off the threadgroove 215 easily.

The disk apparatus in the sixteenth embodiment of the present inventionis provided with a stopper for limiting the moving distance of the nutportion of the rack in the movable direction.

According to the sixteenth embodiment of the present invention,therefore, the nut portion can be prevented surely from going off thefeed screw.

<<Seventeenth Embodiment>>

FIG. 22 is a perspective view of a rack 208 of the disk apparatus in theseventeenth embodiment. In the disk apparatus in the seventeenthembodiment, an adhesive member 222 is filled in the gap of thecantilever parallel spring 221. The adhesive member 222 provides theopen-sided parallel spring 221 with damping characteristics.Consequently, the nut portion 207 can suppress the vibration in theradial direction of the feed screw 215. In the disk apparatus in theseventeenth embodiment, therefore, the nut portion 207 can be fit to thefeed screw 215 more closely, preventing generation of the vibration inthe pick-up base 203.

In the disk apparatus in the seventeenth embodiment, the open-sidedparallel spring provided in the rack is consisting of at least two platesprings and an adhesive member is filled in the gap between the platesprings.

According to the seventeenth embodiment of the present invention,therefore, the nut portion is prevented from vibration and the head isprevented from vibration to be caused by a vibration-like force appliedfrom the feed screw to the nut portion.

<<Eighteenth Embodiment>>

FIG. 23 is a perspective view of a rack 208 of the disk apparatus in theeighteenth embodiment of the present invention.

The rack 208 in the eighteenth embodiment is formed entirely with aresin material including the fixing portion 206, the nut portion 207,the cantilever parallel spring 221, and the stopper 217. Consequently,the rack 208 in the eighteenth embodiment can be formed unitarily, sothat the manufacturing cost is reduced significantly. In the eighteenthembodiment, the shape of the recess 221 a of the cantilever parallelspring is not always rectangular. A corner-rounded square such as anellipse may also obtain the same effect.

In the disk apparatus described in the eighteenth embodiment of thepresent invention, the rack fixing portion, the nut portion, and thecantilever parallel spring are unitarily formed with resin.

According to the eighteenth embodiment of the present invention,therefore, the manufacturing cost of the rack can be reducedsignificantly and the disk apparatus that enables the head to move fastcan be manufactured less expensively.

<<Nineteenth Embodiment>>

FIG. 24 is a perspective view of a nut portion 207 provided in the rackof the disk apparatus of the present invention. FIG. 24 indicates therelationship between dimensions of each portion in the eighteenthembodiment shown in FIG. 23. In FIG. 24, an arrow F indicates a forceapplied to a cantilever parallel spring in the movable direction fromthe thread groove 215. L1 indicates a length of the cantilever parallelspring 221 and L2 indicates a length between the end closer to the nutportion 207 of the cantilever parallel spring 221 and the contactposition between the nut portion 207 and the thread groove 215. Dindicates a gap diameter between two plate springs forming theopen-ended parallel spring 221, t indicates a thickness of the platespring forming the open-ended parallel spring 221, and b indicates awidth of the plate spring of the cantilever parallel spring 221.

The deformation of the cantilever parallel spring 221, when a force isapplied to the nut portion 207, includes both constituent D of the“displacement by parallel movement” and constituent C of the“displacement by bending”. The ratio A between constituent D of the“displacement by parallel movement” and constituent C of the“displacement by bending” is represented by the following equation 1.$\begin{matrix}{A = {{\frac{2}{3} \times \left( {2 + {3 \times \left( \frac{L2}{L1} \right)}} \right) \times \frac{t^{2}}{D \times \left( {D + {2t}} \right)}} \leqq 1.0}} & (1)\end{matrix}$

Next, the source of this equation 1 will be explained. In Chapter 7 ofthe Appendix of “Actual Design/2nd Version” edited by Yotaro Hatamuraand published by Nikkan Kogyo Shinbun-sha, the following equation 2 isdescribed as an equation for representing the ratio B between theconstituent C of the “displacement by bending” and the constituent D ofthe “displacement by parallel movement”. $\begin{matrix}{B = {\frac{2}{3} \times \left( {2 + {3 \times \left( \frac{L2}{L1} \right)}} \right) \times \left( \frac{t}{D} \right)^{2}}} & (2)\end{matrix}$

The constituent C of the “displacement by bending” in the equation 2 isfound by the following equation 3. $\begin{matrix}{C = \frac{F \times {L1}^{2} \times \left( {{3 \times {L2}} + {2 \times {L1}}} \right)}{3 \times E \times b \times t \times D^{2}}} & (3)\end{matrix}$

The constituent D of the “displacement by parallel movement” is foundwith the following equation 4. $\begin{matrix}{D = {\frac{1}{2} \times \frac{F \times {L1}^{3}}{E \times b \times t^{3}}}} & (4)\end{matrix}$

In the equations 2 and 3, F indicates a strength of the force appliedfrom 215 to the nut portion 207. E indicates a vertical elasticitycoefficient of the material of the cantilever parallel spring 221. Inthe equation 3, the thickness t of the plate spring is assumed to bevery thin. Actually, however, as shown in the eighteenth embodiment,when the rack 208 is formed entirely with resin, a certain thickness tmust be given to the plate spring to secure a necessary rigidity.Consequently, this cannot be ignored in the equation. Taking this inconsideration, the constituent C of the “displacement by bending” iscomputed strictly in the following equation 5. $\begin{matrix}{C = \frac{F \times {L1}^{2} \times \left( {{3 \times {L2}} + {2 \times {L1}}} \right)}{3 \times E \times b \times t \times D \times \left( {D + {2 \times t}} \right)}} & (5)\end{matrix}$

The equation 1 is obtained from the equations 4 and 5.

If the constituent C of the “displacement by bending” is larger than theconstituent D of the “displacement by parallel movement”, the use of thecantilever parallel spring 221 will become less effective, and thecharacteristics of the rack will become just equal to the conventionalrack provided with plate springs. More concretely, the teeth 223 are aptto go off the thread groove 215. Especially, in a configuration as shownin the fifteenth embodiment, of the teeth 223 of the nut portion 207 fitin the thread groove 215, only the portion closer to the cantileverparallel spring 221 is worn out in the thread groove 215, degrading thelife of the rack 208 quickly. To avoid such a problem, the constituent Cof the “displacement by bending” should be smaller at least than theconstituent D of the “displacement by parallel movement”. The equation 1indicates a condition on which the rate A between the “displacement bybending” and the “displacement by parallel movement” becomes 1.0 orunder. Naturally, the smaller the constituent C of the “displacement bybending” is with respect to the constituent D of the “displacement byparallel movement”, the better it is. Ideally, the constituent C of the“displacement by bending” should be controlled to 0.1 or under withrespect to the constituent D of the “displacement by parallel movement”.

In the nineteenth embodiment, the L2 size is assumed to be the lengthbetween the end of the cantilever parallel spring 221, closer to the nutportion 207 and the position where the teeth of the nut portion fartherfrom the cantilever parallel spring 221 come in contact with the threadgroove 215. As understood clearly from the equation 1, the larger the L2value is, the larger the rate of “displacement by bending” becomes.Thus, the worst case of the L2 value is taken into consideration todecide the L2 value. In addition, the relationship among sizes in thenineteenth embodiment may be assumed not only for the fifteenthembodiment, but also for other embodiments.

In the case of the disk apparatus in the nineteenth embodiment of thepresent invention, when it is assumed that the length of the cantileverparallel spring provided in the rack is L1, the length between the endof the cantilever parallel spring 221, closer to the nut portion 207 andthe position where the teeth of the nut portion farther from thecantilever parallel spring 221 comes in contact with the thread grooveis L2, the distance between the two plate springs forming the cantileverparallel spring is D, and the thickness of the plate spring is t, therate A between the “constituent of displacement by bending” and the“constituent of displacement by parallel movement” is represented in theequation 6 as shown below. $\begin{matrix}{A = {{\frac{2}{3} \times \left( {2 + {3 \times \left( \frac{L2}{L1} \right)}} \right) \times \frac{t^{2}}{D \times \left( {D + {2t}} \right)}} \leqq 1.0}} & (6)\end{matrix}$

According to the disk apparatus in the nineteenth embodiment of thepresent invention, therefore, the deformation of the cantilever parallelspring of the rack can be controlled to be less. The disk apparatus inthe nineteenth embodiment can thus prevent the nut portion from beingoff the feed screw when the head is accelerated/decelerated suddenly.

<<Twentieth Embodiment>>

FIG. 25 is a perspective view of a portion of the disk near the pick-upin the twentieth embodiment of the present invention.

As shown in FIG. 25, a shaft holder 220 is provided on the pick-up base203 of the disk apparatus in the twentieth embodiment. One end of theshaft holder 220 is fixed to the pick-up base 203 and the other endpresses the second guide shaft 210 that slides in the guiding groove213. The position where the shaft holder 220 presses the second guideshaft 210 is a position separated on one side from the guiding groove213 in the axial direction of the second guide shaft 210.

Since such a shaft holder 220 is provided, a force is applied to thepick-up base 203 so that the pick-up base is twisted around the guidegroove 213. Consequently, the pick-up base 203 in the disk apparatusdescribed in the twentieth embodiment is inclined to provide a playbetween the guide hole 212 and the guide shaft 209 or to eliminate theplay from between the guide groove 213 and the guide shaft 210.

The vibration generated in the pick-up base 203 when the pick-up base203 is accelerated/decelerated suddenly can be suppressed effectively.

The contact status between the pick-up base 203 and the guide mechanism211 is changed by the following relationship when the shaft holder 220is provided; the relationship between the guide hole 212 and the guidegroove 213, the diameter of the guide hole 212 and the diameter of theguide shaft 209, the length of the narrow contact portion of the guidegroove 213 and the diameter of the guide shaft 210, or the relationshipbetween the pick-up 202 and the pick-up base 203.

FIGS. 26 and 27 indicate how the pick-up base 203 is in contact with theguide mechanism 211 when the shaft holder 220 is provided. FIG. 26 is across sectional view of the pick-up base 203 when it is seen from thedirection of the guide groove 213. As shown in FIG. 26, the first guideshaft 209 is inclined to the guide hole 212 to come in compact with eachother. The first guide shaft 209 is in contact with the guide hole 212with no excessive play.

FIG. 27 is a side cross sectional view of the pick-up base 203 when itis seen from the direction of the guide groove 213. As shown in FIG. 27,the second guide shaft 210 is inclined to the guide groove 213 to comein contact with each other. The second guide shaft 210 is always incontact with the guide groove without an excessive play.

The shaft holder 220 in the twentieth embodiment presses a positionseparated from the guide groove on one side in the radial direction ofthe second guide shaft 210. As a result, the second shaft 210 receives arotary moment around the guide groove 213 due to the pressure of theshaft holder 220. And, the pick-up base 213 is inclined to the secondguide shaft 210 due to the rotary moment. Consequently, the further theposition where the shaft holder 220 presses the second guide shaft 210is separated from the guide groove 213, the more effectively the shaftholder 220 can press the pick-up base 203 against the guide mechanism211 with a less force.

In the disk apparatus in the twentieth embodiment shown in FIG. 25, theshaft holder 220 is consisting of a plate spring. However, the shaftholder 220 is not limited only to such a plate spring. It may be anotherelastic material such as a coil spring to obtain the same effect.

The disk apparatus in the twentieth embodiment of the present inventioncomprises a pick-up for reading and writing signals from and on disk; apick-up base provided with the pick-up; the first guide shaft fit in aguide hole provided in the pick-up base and used to guide the pick-upbase slidably in the radial direction of the disk; the second guideshaft fit in a guide groove provided in the pick-up base and used tolimit the rotation of the pick-up base around the guide shaft; and ashaft holder fixed to the pick-up base at one end to be pressed againstthe second guide shaft at a position where the other end is separatedfrom the guide groove on one side in the radial directions of the secondguide shaft, and forcing the pick-up base in the direction where theinside face of the guide groove is in contact with the second guideshaft.

According to the twentieth embodiment of the present invention,therefore, the guide hole of the pick-up base or the gap between theguide groove and the guide shaft can be eliminated without increasingthe frictional load of rotation. According to the twentieth embodiment,vibration of the pick-up base can thus be suppressed even when thepick-up base is accelerated/decelerated suddenly, and accordingly, it ispossible to realize a disk apparatus whose pick-up can be moved fast.

<<Twenty-first Embodiment>>

FIG. 28 is a perspective view of a portion of the disk apparatus, closeto the pick-up of the disk apparatus in the twenty-first embodiment ofthe present invention.

As shown in FIG. 28, the cantilever parallel spring 221 of the rack 208in the disk apparatus in the twenty-first embodiment can be moved inparallel to the recording face of the disk and in the radial directionof the feed screw 205. On the other hand, the shaft holder 220 pressesthe second guide shaft 210 vertically to the recording face of the disk.

In the twenty-first embodiment, the movable direction of the cantileverparallel spring 221 of the rack 208 is decided to become orthogonal tothe pressing direction of the shaft holder 220 such way, so that theexcessive play between the pick-up base 203 and the guide mechanism 211can be eliminated in every direction. Thus, even when the pick-up base203 is accelerated/decelerated suddenly for movement, the vibration inthe pick-up base 203 can be reduced significantly. The disk apparatus inthe twenty-first embodiment can thus record/play back informationstably.

There is another embodiment for obtaining the same effect as that in thetwenty-first embodiment; the movable direction of the cantileverparallel spring 221 of the rack 208 in the twenty-first embodiment shownin FIG. 28 is decided as another direction, for example, the movabledirection of the cantilever parallel spring 221 is decided to bevertical to the recording face of the disk and the pressing direction ofthe shaft holder 220 is decided to be parallel to the recording face ofthe disk.

The disk apparatus in the twenty-first embodiment of the presentinvention comprises a pick-up for reading/writing signals on/from adisk; a pick-up base provided with the pick-up; a traverse motor formoving the pick-up in the radial direction of the disk; a feed screwrotated by the traverse motor and provided with a thread groove on itsouter periphery; a rack provided with a fixing portion fixed to thepick-up base, a nut portion fit in the thread groove, and an cantileverparallel spring for connecting the fixing portion to the nut portion;the first guide shaft for guiding the pick-up slidably in the radialdirection of the disk; the second guide shaft fit in the guide grooveprovided in the pick-up base and used for limiting the rotation of thepick-up base around the first guide shaft; and a shaft holder fixed tothe pick-up base at one end and being pressed against the second guideshaft at a position where the other end is separated from the guidegroove on one side in the radial direction of the second guide shaft,and forcing the pick-up in the direction where the inside face of theguide groove is in contact with the second guide shaft. In the diskapparatus in the twenty-first embodiment, the displaceable direction ofthe cantilever parallel spring is orthogonal to the direction in whichthe shaft holder is pressed against the second guide shaft.

According to the disk apparatus in the twenty-first embodiment of thepresent invention, therefore, the nut portion of the rack is never offthe feed screw and the force applied to the pick-up base from the nutportion is suppressed by the cantilever parallel spring and the shaftholder of the rack in every direction. And accordingly, vibration of thepick-up can be suppressed and the pick-up can be moved fast even whenthe pick-up is accelerated/decelerated suddenly.

Since each of the disk apparatuses in the fourteenth to twenty-firstembodiments of the present invention is formed as explained above, thenut portion of the rack is not disengaged from the feed screw andvibration of the pick-up base can be reduced significantly even when thepick-up base is accelerated/decelerated suddenly. In addition, in eachof the above-mentioned configurations, because the sliding load betweenthe nut portion and the feed screw, as well as between the pick-up baseand the guide shaft is not increased so much, it is no need to increasethe torque of the traverse motor.

In each of the disk apparatuses described in the fourteenth totwenty-first embodiments of the present invention, the pick-up base canbe moved fast for stable and fast accessing without increasing themanufacturing cost. Thus, the disk apparatus is very effective inindustrial fields.

<<Twenty-second Embodiment>>

Next, the disk apparatus in the twenty-second embodiment of the presentinvention will be explained.

In recent years, high speed accessing performance is required for diskapparatuses to feed the pick-up to a target position on the diskquickly, and a disk apparatus that uses a stepping motor as a means ofmoving the pick-up is already commercialized. Generally, two operationsare needed to move the pick-up in a disk apparatus; playback operationand access operation. When in a playback operation, the pick-up followsup helically-formed tracks on the disk, so the stepping motor must berotated slowly to move the pick-up gradually. When in an accessoperation, the pick-up is moved to a target position in a moment, so thestepping motor must be rotated fast. In such a disk apparatus that usesa stepping motor for moving the pick-up, the stepping motor is rotatedin two ways; high speed and low speed. Thus, the rotation must bechanged over between those two speeds.

[General Stepping Motor Controlling Method]

Hereunder, a general stepping motor controlling method will be explainedwith reference to FIGS. 29, 30, and 31 showing a simplified insideconfiguration of a general stepping motor.

FIG. 29 is a simplified inside configuration of a general steppingmotor. In FIG. 29, the arrow 502 a indicates the direction of a currentflowing in the A-phase coil and the arrow 502 b indicates the directionof a current flowing in the B-phase coil.

In FIG. 29, a rotator 502 c has a plurality of pairs of N and S poles.The point P on the rotator begins rotating when the current 502 aflowing in the A-phase coil and the current 502 b flowing in the B-phasecoil are changed together and stops at a position where the balancebetween the magnetic force generated from the coils and the frictionalload of rotation is stabilized. A stepping motor has some mechanicalstability positions. Positions 502W, 502X, 502Y, and 502Z representcontinuous four mechanical stability positions of those mechanicalstability positions of the stepping motor. The number of pairs ofmagnetic poles and the number of mechanical stability points differamong types of stepping motors.

FIG. 30 is a wave form chart indicating the driving signal pattern 1 ofthe general stepping motor. FIG. 30 is the driving signal pattern of aso-called 2-phase excitation type general stepping motor. This drivingsignal pattern is used in many cases for rotating a stepping motor fast.

In FIG. 30, the wave form 503A represents the voltage wave form of theA-phase coil of the stepping motor. The wave form 403B indicates thevoltage wave form of the B-phase coil. In such a 2-phase excitation typestepping motor, the voltage of each coil is repeated cyclically among 4states (503W, 503X, 503Y, and 503Z). In the state 503W, the point Pshown in FIG. 29 is moved to the position 502W. In the same way, in thestates 503X, 503Y, and 503Z shown in FIG. 30, the point shown in FIG. 29is moved to the positions 502X, 502Y, and 502Z respectively.

FIG. 31 is a wave form chart indicating the driving signal pattern 2 ofthe general stepping motor. This driving signal pattern 2 is applied tothe 2-phase excitation type stepping motor as a method for changingdriving signals at a fixed inclination to the time, as shown in FIG. 31.The driving signal pattern 2 is suitable for rotating a stepping motorslowly. In FIG. 31, the wave form 504A indicates the voltage of theA-phase coil of a stepping motor and the wave form 504B indicates thevoltage of the B-phase coil. In the state 504W shown in FIG. 31, thepoint P shown in FIG. 29 is moved to the position 502W. In the same way,in the states 504X, 504Y, and 504Z shown in FIG. 31, the point P shownin FIG. 29 is moved to the positions 502X, 502Y, and 502Z respectively.

FIG. 32 is a wave form chart indicating the driving signal pattern 3 ofthe general stepping motor. The driving signal pattern of FIG. 32 is aso-called micro-step excitation method stepping motor and this drivingsignal pattern is often used for rotating a stepping motor step by stepvery slowly at fine pitches. In FIG. 32, the wave form 505A indicatesthe voltage wave form of the A-phase coil of a stepping motor and thewave form 505B indicates the voltage wave form of the B-phase coil ofthe stepping motor. Since a micro-step excitation method has manyexcitation states, the inner state of the stepping motor is controlledusing, for example, phase numbers (Ph00, Ph01, . . . ) as shown in FIG.32. In FIG. 32, 32 phases given with phase numbers within Ph00 to Ph31are used. The driving signal pattern can be changed cyclically byincreasing/reducing the phase number one by one. In addition, to findvoltage wave forms 505A and 505B of the coils with respect to phasenumbers, a table of trigonometric function constants is provided in astoring means such as ROM and RAM in advance and a voltage is decidedwith reference to the voltage value corresponding to each phase numberin the table. In the state 505W (phase number Ph00) shown in FIG. 32,the point P shown in FIG. 29 is moved to the position 502W. In the sameway, in the states 505X (phase number Ph08), 505Y (phase number PH16),and 505Z (phase number Ph24) shown in FIG. 32, the point P shown in FIG.29 is moved to the positions 502X, 502Y, and 502Z respectively.

[Problems in Changing Operation for Driving Signal Patterns]

The above-mentioned stepping motor controlling method is confronted withthe following problems, however. For example, when an accessingoperation is performed during a playback operation in a disk apparatus,the driving signal pattern 2 or 3 for slow operation shown in FIG. 31 orFIG. 32 must be changed to the driving signal pattern 1 for fastrotation shown in FIG. 30.

Next, such a change-over problem will be explained with reference toFIG. 33. FIG. 33 is a wave form chart indicating the general drivingsignal pattern 1. FIG. 33 indicates how the driving pattern 2 for slowrotation shown in FIG. 31 is changed to the driving signal pattern 1 forfast rotation shown in FIG. 30. In FIG. 33, the wave form 506A indicatesthe voltage wave form of the A-phase of a stepping motor and the waveform 506B indicates the voltage wave form of the B-phase coil. In theslow rotation part shown in FIG. 33, the state is being changed from506W to 506X. This state corresponds to the slow rotation of the point Pshown in FIG. 29 from the position 502W to the position 502X.

When the rotation speed is changed from slow to fast during an operationby the conventional method, the state 506X pattern shown in FIG. 33 isoutput as the first driving signal for the fast rotation. However, thepoint P shown in FIG. 29 is already moved close to the position 502Xslowly just before the speed change. Thus, almost no rotation is madewith respect to the 506X driving signal shown in FIG. 33, which movesthe point P to the position 502X. Consequently, the first state 506Xdriving signal pattern after the change to fast rotation is redundantand less effective for accelerating the rotation of the stepping motor.When the conventional driving signal changing method is used to changethe driving signal, therefore, the accelerating time for fast rotationof the stepping motor becomes long.

As mentioned above, in the case of the conventional driving signalchanging method, as the first state in the driving signal for fastrotation after a speed change is output a signal pattern for moving therotator to the nearest mechanical stability position in the rotatingdirection of the stepping motor. Consequently, when the rotator is movedup to a position near a mechanical stability point during a slowrotation, a driving signal pattern is output to move the rotator to thesame mechanical stability position in fast rotation. Thus, anunnecessary state is generated during a driving signal change, and theuse of this driving signal changing method for a disk apparatus causesthe access operation to be delayed.

[Problems in Changing method of Driving Signal Pattern in Micro-stepExcitation System]

Next, problems to arise from the conventional changing method in themicro-step excitation system will be explained with reference to FIG.34.

FIG. 34 is a wave form chart indicating the conventional driving signalchange pattern 2. FIG. 34 indicates a changing condition from theconventional driving signal pattern 3 for slow rotation shown in FIG. 32to the conventional driving signal pattern 1 for fast rotation shown inFIG. 30. In FIG. 34, the wave form 507A indicates the voltage wave formof the A-phase of the stepping motor and the wave form 507B indicatesthe voltage wave form of the B-phase coil. The slow rotation part inFIG. 34 indicates that the state is being changed from 507W to 507X.This means that the state is changed from Ph00 to Ph07. This operationcorresponds to an operation in which the point P shown in FIG. 29 isbeing rotated slowly from the position 502W to the position 502X. Whenthe rotation speed is changed from slow to fast during an operation bythe conventional method here, the state 507X pattern shown in FIG. 34 isoutput as the first driving signal for the fast rotation. However, thepoint P shown in FIG. 29 is already moved to Ph07, that is, a positionnear 502x with a slow rotation just before the signal change. Thus,almost no rotation is made with respect to the 507X driving signal shownin FIG. 34, used to move to the position 502X. The first state 507Xdriving signal pattern, after the change to fast rotation, is only achange from Ph07 to Ph08. So, it is redundant and less effective foraccelerating the rotation of the stepping motor. The accelerating timethus becomes long for the fast rotation of the stepping motor.

Under such the circumstances, it is an object of the disk apparatus inthe twenty-second embodiment of the present invention to solve theabove-mentioned problems in the conventional apparatus and shorten theaccelerating time for fast rotation of the stepping motor moresignificantly than the conventional method without generating anyredundant state when the rotation speed of the stepping motor is changedfrom slow to fast.

In order to solve the above-mentioned problems, the stepping motorcontrolling method in the twenty-second embodiment comprises a means ofgenerating the first driving signal for slow rotation of the steppingmotor; a means of generating the second driving signal for fast rotationof the stepping motor; and a means of controlling switching between thefirst and second driving signal generating means. When changing therotation speed of the stepping motor from slow to fast, the controllingmeans decides whether or not the rotator of the stepping motor existsnear a mechanical stability position of the stepping motor according tothe voltage value of the driving signal output from the first drivingsignal generating means or the state number owned by the first drivingsignal generating means. And, the controlling means outputs a command tothe second driving signal generating means when the rotator exists neara mechanical stability position. After the second driving signal meansoutputs a driving signal for rotating the stepping motor to the nextmechanical stability position in the rotating direction of the steppingmotor, the controlling means changes the signal generating means fromthe first driving signal generating means to the second driving signalgenerating means.

Consequently, the driving signal used to change the rotation speed tofast using the stepping motor controlling method in the twenty-secondembodiment of the present invention can move the rotator of the steppingmotor to the mechanical stability position one more ahead than theconventional method within the same time.

Hereunder, the principle of the above-mentioned operation will beexplained with reference to FIG. 35. FIG. 35 is a characteristic chartindicating the relationship between position and torque of a steppingmotor. In FIG. 35, the horizontal axis indicates the position of point Pshown in FIG. 29. The position 508X in FIG. 35 indicates that the pointP in FIG. 29 exists at the position 502X. In the same way, the positions508W and 508Y on the horizontal axis in FIG. 25 indicate that the pointP shown in FIG. 29 will exist at positions 502W and 502Y respectively.

The vertical axis in FIG. 35 indicates a torque generated in thestepping motor when each coil of the stepping motor is excited by thedriving signal of the state 503Y shown in FIG. 30.

The torque in the forward direction on the vertical axis in FIG. 35indicates the size of the torque for moving the rotator on thehorizontal axis to the right. Thus, when the rotator exists at theposition 508X in FIG. 35, the rotator can be moved to the position 508Ywith the largest torque received. This means that when the point P shownin FIG. 29 exists at the position 502X, it receives the largest torqueand accordingly, the point P can be moved to the position 502Y. In otherwords, the torque of the stepping motor with respect to a fixed drivingsignal is decided by the position of the rotator.

To move the pick-up, etc. by rotating the stepping motor fast at thistime, the torque must be over a certain strength. When a torque over avalue needed for a fast rotation can be generated, the rotator of thestepping motor can be moved from the position 508X to the position 508Yshown in FIG. 35. This necessary torque strength is shown with a dottedline in FIG. 35. When the torque generated in a stepping motor iscompared with the torque needed for the fast rotation in FIG. 35, it isfound that a torque can be generated over the fast rotation torque evenwhen the rotator goes off the position 508X slightly. In other words,within the range between the positions 508XA and 508XB shown in FIG. 35,the rotator can be moved fast to the position 508Y.

In the case of the stepping motor controlling method in thetwenty-second embodiment of the present invention, the position to whichthe rotator reaches slowly is decided just before the stepping motor isrotated fast. Then, if the rotator reaches a position near a mechanicalstability position, that is, within the positions 508X to 508Y shown inFIG. 35, no driving signal is output to move the rotator to the firstmechanical stability position 508X, but a driving signal is output tomove the rotator to the next mechanical stability position 508Y as thefirst driving signal for fast rotation. Consequently, the acceleratingtime for rotating the stepping motor fast can be shortened moresignificantly than the conventional method.

Hereunder, the twenty-third and twenty-fourth embodiments will beexplained with reference to the attached drawings. Those embodimentsexplain the stepping motor controlling method in the twenty-secondembodiment of the present invention more in detail.

<<Twenty-third Embodiment>>

FIG. 36 is a block diagram for a control circuit of a stepping motor towhich the stepping motor controlling method in the twenty-thirdembodiment of the present invention is applied. Hereunder, the steppingmotor controlling method in the twenty-third embodiment will beexplained with reference to FIG. 36.

In FIG. 36, the first driving signal generating means 501A generatesdriving signals for rotating the stepping motor as shown in FIG. 31slowly. The first driving signal generating means 501A outputs thedriving signals 501H and 501J for driving the A-phase coil and theB-phase coil of the stepping motor respectively. The second drivingsignal generating means 501B generates driving signals for rotating thestepping motor as shown in FIG. 30 fast. The second driving signalgenerating means 501B outputs driving signals 501K and 501L for drivingthe A-phase coil and the B-phase coil of the stepping motorrespectively. The driving signals 501H and 501K are connected to thefirst switch 501C and the driving signals 501J and 501L are connected tothe second switch 501D respectively.

The controlling means 501E outputs a command signal 501N to change thestatus of the first driving signal generating means 501A. Thecontrolling mans 501E outputs a command signal 501P to change the statusof the second driving signal generating means 501B. The controllingmeans 501E also outputs a change-over signal 501M to change over boththe first switch 501C and the second switch 501D at the same time.Consequently, the controlling means 501E selects the driving signal fromeither the first driving signal generating means 501A or the seconddriving signal generating means 501B to output the driving signals 501Qand 501R. The driving signals 501Q and 501R are entered to the firstexciting means 501F and the second exciting means 501G respectively. Thefirst exciting means 501F and the second exciting means 501G amplify thedriving signals 501Q and 501R to excite the A-phase and B-phase coils(501S) and (501T) of the stepping motor.

FIG. 37 is a wave form chart indicating a driving signal change-overpattern in the twenty-third embodiment of the present invention. In FIG.37, the wave form 509A indicates the voltage wave form of the A-phasecoil of the stepping motor and the wave form 509B indicates the voltagewave form of the B-phase coil of the stepping motor. The driving signalchange-over pattern shown in FIG. 37 indicates that the stepping motoris controlled to be changed from slow to fast.

The slow rotation portion indicates a state change of the driving signalpattern 2 shown in FIG. 31 from 504W to 504X, corresponding to the statechange from 509W to 509X shown in FIG. 37. This slow rotation portioncorresponds to a slow movement of the point P shown in FIG. 29 from theposition 502W to the position 502X.

The fast rotation portion indicates the states 503Y and 503Z of thedriving signal pattern 1 shown in FIG. 30, corresponding to the states509Y and 509Z shown in FIG. 37. This fast rotation portion correspondsto a movement of the point P shown in FIG. 29 to the position 502Y, thento the position 502Z.

Next, the operation of the disk apparatus in the twenty-third embodimentof the present invention will be explained with reference to FIGS. 29,35, 36, and 37.

In FIG. 36, the controlling means 501E controls the first switch 501Cand the second switch 501D using the change-over signal 501M. Thecontrolling means 501E selects the driving signals 501H and 501J outputfrom the first driving signal generating means 501A to rotate thestepping motor slowly. When the rotation speed of the stepping motormust be changed from slow to fast in such a case, the controlling means501E compares the comparison level held in the controlling means 501Eitself with the voltage of the driving signal 501H or 501J, whichever isbeing changed. This comparison level is used as a comparing value todecide whether or not the rotator is within the positions 508XA to 508XBshown in FIG. 35. This comparing value can be decided by the mechanicalsliding load with respect to the torque of the stepping motor in thedesigning stage.

According to the result of the comparison, the controlling means 501Eoutputs a command signal 501P to decide the status of the second drivingsignal generating means 501B. At the same time, the controlling means501E changes over the first switch 501C and the second switch 501D usingthe change-over signal 501M to select the driving signals 501K and 501Loutput from the second driving signal generating means 501B.

The above-mentioned selecting operation will be explained more in detailwith reference to FIG. 37.

FIG. 37 indicates that the B-phase coil voltage wave form 509B is beingchanged during a slow rotation, but not enters the state 509X yetcompletely when the rotation speed is changed to fast. In other words,in FIG. 29, the point P is being rotated slowly from the position 502Wto the position 502X, and not reaches the position 502X yet.

In the conventional driving signal change-over pattern, the state 506Xpattern is output as the first driving signal in a fast rotation asshown in FIG. 33. In other words, in a slow rotation just before it ischanged to a fast rotation, unless the point P reaches the position 502Xshown in FIG. 29, the point P is rotated to the position 502X shown inFIG. 29 completely with the first driving signal after the rotationspeed is changed to fast, then the point P is rotated to the position502Y.

On the contrary, in the twenty-third embodiment of the presentinvention, comparison levels 509SA and 509SB as shown in FIG. 37 areprovided. The comparison levels are used to compare the voltage of eachcoil whose voltage is changed during a slow rotation with 509SA or 509SBto decide whether or not the point P shown in FIG. 29 is between thepositions 508XA and 508XB shown in FIG. 35. If the voltage of a coil ischanged from negative to positive during a slow rotation, the coilvoltage is compared with the comparison level 509SA. If the coil voltageis greater than 509SA, the point shown in FIG. 29 exists betweenpositions 508XA and 508XB shown in FIG. 35. If the coil voltage ischanged from positive to negative during a slow rotation, the coilvoltage is compared with the comparison level 509SB. And, if the coilvoltage is lower than the 509SB, the point shown in FIG. 29 existsbetween positions 508XA and 508XB shown in FIG. 35.

If the point P shown in FIG. 29 exists between the positions 508XA and508XB shown in FIG. 35, it is possible to generate a torque necessaryfor a fast rotation of the rotator to the next position 508Y. In otherwords, the driving signal needed in the conventional method to rotatethe point P shown in FIG. 29 to the position 502X completely can beeliminated in this embodiment. Consequently, in the stepping motorcontrolling method in the twenty-third embodiment, the first drivingsignal in a fast rotation is not the driving signal for moving the pointP to the position 502X, but it is the driving signal for moving thepoint P to the position 502Y.

In the case shown in FIG. 37, because the B-phase coil voltage wave form509B is smaller than that of the comparison level 509SB when therotation speed is changed, the state 509Y can be used for the firstdriving signal in a fast rotation. And, to generate the driving signalof this state 509Y, the controlling means 501E shown in FIG. 36 issues acommand signal 501P to decide the status of the second driving signalgenerating means 501B.

When the controlling method in the twenty-third embodiment shown in FIG.37 is compared with the conventional controlling method shown in FIG. 33taking the above-mentioned into consideration, the controlling methodshown in FIG. 37 can make the point P advance one position ahead withinthe same time. Consequently, the stepping motor controlling method inthe twenty-third embodiment can accelerate the stepping motor quicklymore than the conventional controlling method.

According to the twenty-third embodiment of the present invention,therefore, when the driving signal of the stepping motor is changed fromslow to fast, the driving signal voltage is compared with the comparisonlevel, so that the position of the stepping motor rotator is decided andthe fast rotation driving signal can be issued one more state ahead thanthe conventional controlling method. The stepping motor controllingmethod in the twenty-third embodiment can thus accelerate the steppingmotor more quickly than the conventional controlling method.

<<Twenty-fourth Embodiment>>

FIG. 38 is a wave form chart indicating a driving signal change-overpattern in the stepping motor controlling method defined in thetwenty-fourth embodiment of the present invention.

In FIG. 38, the wave form 510A indicates the voltage wave form of theA-phase coil of the stepping motor and the wave form 510B indicates thevoltage wave form of the B-phase coil of the stepping motor. The drivingsignal change-over pattern shown in FIG. 38 indicates a change of thestepping motor control from slow rotation to fast rotation. The slowrotation part indicates a change of the conventional driving signalpattern shown in FIG. 32 from the state 505W (phase number Ph00) to thestate 505X (phase number Ph08), corresponding to the change from thestate 510W to the state 510X in FIG. 38. This slow rotation partcorresponds to the slow movement of the point P shown in FIG. 29 fromthe position 502W to the position 502X. The fast rotation part indicatesthe states 503Y and 503Z of the conventional driving signal pattern 1shown in FIG. 30, corresponding to the states 510Y and 510Z shown inFIG. 38. This fast rotation part corresponds the movement of the point Pshown in FIG. 29 to the position 502Y, then to the position 502Z.

Next, the operation of the stepping motor in the twenty-fourthembodiment of the present invention as explained above will be explainedwith reference to FIGS.29, 32, 35, 36, and 38.

In FIG. 36, the controlling means 501E controls the first switch 501Cand the second switch 501D using the change-over signal 501M to selectthe driving signals 501H and 501J output from the first driving signalgenerating means 501A to rotate the stepping motor slowly in thetwenty-fourth embodiment.

If the rotation speed of the stepping motor must be changed from slow tofast in such a case, the controlling means E decides whether or not thephase number of the first driving signal generating means 501A is near amechanical stability position. This phase number can be used to know theinside status of the first driving signal generating means 501A usingthe command signal 501N.

For example, the state 505X (phase number Ph08) indicates in FIG. 32that the point P shown in FIG. 29 is at the mechanical stabilityposition 502X. The phase numbers Ph07 and Ph09 which are positioned onephase number before and after the phase number Ph08 shown in FIG. 32,indicate that the point P shown in FIG. 29 is positioned near amechanical stability position 502X. In other words, it can be decided bythe phase number whether or not the rotator of the stepping motor existswithin the positions 508XA to 508XB shown in FIG. 35. This is also truefor other mechanical stability positions. The phase numbers Ph15 andPh17, which are one phase number before and after the state 505Y (phasenumber PH16) shown in FIG. 32, indicate that the point P exists near amechanical stability position.

The correspondence between the range within positions 508XA to 508XBshown in FIG. 35 and the range of phase numbers shown in FIG. 32 can bedecided by the micro-step resolution and the mechanical sliding loadwith respect to the stepping motor torque in the designing stage.

According to the comparison between phase numbers, the controlling means501E outputs a command signal 501P to decide the status of the seconddriving signal generating means 501B and changes over the first switch501C and the second switch 501D using the change-over signal 501M toselect the driving signals 501K and 501L output from the second drivingsignal generating means 501B.

Although the B-phase coil voltage wave form 510B is being changed duringa slow rotation in FIG. 38, the point P is not rotated to the state 510X(Ph08) completely yet when the rotation speed is changed from slow tofast. In other words, the point P shown in FIG. 29 is being changed fromthe position 502W to the position 502X slowly and not reach the position502X completely yet.

In the conventional driving signal change pattern, the state 507Xdriving signal is output as the first driving signal in a fast rotationas shown in FIG. 34. In other words, in a slow rotation just beforebeing changed to a fast rotation, unless the point P shown in FIG. 29reaches the position 502X completely, the point P is rotated to theposition 502X completely with the first driving signal for a fastrotation, then rotated to the next position 502Y.

On the contrary, in the twenty-fourth embodiment of the presentinvention, if the rotation speed is changed from slow to fast before thepoint P reaches the state 510X (phase number Ph08) in a slow rotation asshown in FIG. 38, phase numbers are compared to know whether or not Ph07or Ph09, which is before or after the phase number Ph08, is alreadyreached. With this, it can be decided whether or not the point P shownin FIG. 29 exists between the positions 508XA and 508XB shown in FIG.35.

In the case shown in FIG. 38, when the rotation speed is changed, thepoint P shown in FIG. 29 already reaches Ph07, so the state 510Y can beused as the first driving signal for a fast rotation. To generate thisstate 510Y driving signal, the controlling means 501E shown in FIG. 36decides the status of the second driving signal generating means 501Busing the command signal 501P.

When the controlling method in the twenty-fourth embodiment shown inFIG. 38 is compared with the conventional controlling method shown inFIG. 34 taking the above-mentioned into consideration, the controllingmethod shown in FIG. 38 can make the point P advance one position aheadwithin the same time. Consequently, the stepping motor controllingmethod in the twenty-fourth embodiment can accelerate the stepping motormore quickly than the conventional controlling method.

According to the twenty-fourth embodiment of the present invention,therefore, when the driving signal of the stepping motor is changed fromslow to fast, the phase numbers of the driving signal generating meansare compared to decide the position of the stepping motor rotator, sothat the fast rotation driving signal can be started one more stateahead than the conventional controlling method. Thus, the stepping motorcontrolling method in the twenty-fourth embodiment can accelerate thestepping motor more quickly than the conventional controlling method.

The stepping motor controlling methods in the twenty-third andtwenty-fourth embodiments may also be formed with software instead of acircuit as shown in FIG. 36. If such the software is used, the excitingmeans 501F and 501G, the A-phase coil (501S), and the B-phase coil(501T) shown in FIG. 36 are formed with a circuit respectively, butother items may be formed with the software incorporated in anarithmetic operation LSI such as a microcomputer and a DSP (Digitalsignal processor) respectively.

As explained in the twenty-third and twenty-fourth embodiments, thecontrolling means 501E executes processings to form driving signalpatterns, compare/compute driving signals, decide phase numbers, andchange over driving signal patterns to output the voltage value of eachdriving signal, which becomes the final computation result, to theexciting means 501F and 501G as a digital signal. The exciting means501F and 501G converts the voltage values of those digital signals toanalog signals via a PWM converter and a D/A converter, then amplifiesthe analog signals to excite object coils.

In the twenty-second to twenty-fourth embodiments of the presentinvention, therefore, it is decided whether or not the rotator of thestepping motor is positioned near a mechanical stability position of thestepping motor according to the voltage value of the driving signal in aslow rotation or the state number owned by the driving signal generatingmeans when the control of the stepping motor is changed from slow tofast rotation. When the rotator of the stepping motor is positioned neara mechanical stability position, the controlling means 501E outputs adriving signal for rotating the stepping motor to the next mechanicalstability position of the above-mentioned mechanical stability positionin the rotating direction of the stepping motor.

According to the controlling method in the twenty-second totwenty-fourth embodiments, therefore, the driving signal, after therotation of the stepping motor is changed from slow to fast, can movethe rotator of the stepping motor to a mechanical stability position onemore ahead than the conventional controlling method within the sametime. As a result, the controlling method in the twenty-second totwenty-fourth embodiments can accelerate the stepping motor more quicklythan the conventional controlling method.

When any of the stepping motor controlling methods defined in thetwenty-second to twenty-fourth embodiments of the present invention isused for a disk apparatus, it is possible to obtain an effect that thedisk apparatus access time can be shortened significantly.

<<Twenty-fifth Embodiment>>

In recent years, high speed accessing performance is required for diskapparatuses to feed the pick-up to a target position on the diskquickly. A disk apparatus that uses a stepping motor as a traverse motorfor feeding the pick-up is already commercialized. Since the steppingmotor is rotated in units of a fixed step angle with respect to thedriving pulses, it is easy to open-control the feeding distance of thepick-up and it needs no position detecting means. When using such astepping motor for a disk apparatus, therefore, the pick-up feedingmechanism can be simplified. In addition, since the stepping motor isrotated synchronously with the frequency (pulse rate) of the drivingpulses, it is easy to control the rotation speed of the stepping motor.

Hereunder, a conventional disk apparatus will be explained withreference to the attached drawings. FIG. 39 is a block diagram for aconfiguration of the conventional disk apparatus. FIG. 40 is a wave formchart indicating a frequency change (pulse rate pattern) of the drivingpulses in the prior art.

In FIG. 39, a disk 601 having a helically-formed information tracks isrotated by a spindle motor 602. On/from the disk 601 is recorded/playedback information via a pick-up 603. The pick-up 603 is provided with alens 604. This lens 604 is provided movably by a focus actuator and atracking actuator (both not illustrated) incorporated in the pick-up 603magnetically in both vertical and horizontal directions. A focus servomeans 605 drives the focus actuator according to the focus error signalindicating a displacement value of the lens 604 from the disk 601 sothat the lens 604 is kept away by a fixed distance from the disk 601.The tracking servo means 606 drives the tracking actuator so that thelens 604 follows up a given information track on the disk 601 accordingto the tracking error signal indicating a displacement value of the lens604 from the center of the tracks on the disk 601. The spindle motor 607moves the pick-up 603 in the radial direction of the disk 601. Thestepping motor driving means 608 applies a driving voltage to thestepping motor 607. The pick-up position detecting means 609 detects thecurrent position of the pick-up 603 from the address informationincluded in the data read by the pick-up 603. The pulse counting means610 counts the number of pulses for driving the stepping motor necessaryto move the pick-up 603 from the current position of the pick-up 603detected by the pick-up position detecting means 609 to a target addressentered from an external device. The pulse rate pattern creating means611 creates a frequency change (pulse rate) pattern of the input pulses,entered to the stepping motor driving means 608, according to the numberof pulses counted by the pulse counting means 610. A feed screw 612holds the pick-up 603 movably in the radial direction of the disk 601and transmits the torque of the stepping motor 607 to the pick-up 603.

Next, the operation for moving the pick-up 603 fast in a general diskapparatus formed as explained above will be explained.

The lens 604 is controlled by the focus servo means 605 and the trackingservo means 606 so that it can read information from the disk 601 viathe pick-up 603. The focus servo means 605 controls the lens 604 so thatthe lens 604 can be kept focused on the disk 601. In addition, thetracking servo means 606 is controlled by an electromagnetic actuator(not illustrated) so that the lens 604 can keep following up the targettrack on the disk 601.

To access a given track, the pulse counting means 610 counts the numberof pulses necessary to move the pick-up 603 from the current positiondetected by the pick-up position detecting means 609 to a targetposition. Then, the tracking servo means 606 is stopped and the pulserate pattern creating means 611 creates a pulse rate as shown in FIG. 40and outputs the pulse rate to the stepping motor driving means 608. Thepulse rate shown in FIG. 40 is a general driving signal pattern fordriving the stepping motor 607. The stepping motor driven by thestepping motor driving means 608 at this pulse rate moves the pick-up603. After the pick-up 603 reaches a specified position, the trackingservo means 606 is started again to record information.

The pulse rate shown in FIG. 40 is output from the pulse rate patterncreating means 611 being composed of a microcomputer, etc. Next, thepulse rate created by the pulse rate pattern creating means 611 will beexplained.

As shown in the pulse rate in FIG. 40, an output is started at a speedthat the stepping motor 607 can start up without stepping it out. (Sucha speed is referred to as a self-starting frequency, which is indicatedwith the level P1 in FIG. 40). A step-out mentioned here means thestatus of abnormal rotation of the stepping motor, caused when thestepping motor 607 go out of step with the entered pulse rate.

After this, the pulse rate is raised at a fixed pulse rate change rateuntil a desired speed (frequency indicated with P2 in FIG. 40) isreached. After the stepping motor is rotated at the frequency speedindicated with P2 for a specified time, the pulse rate is lowered so asto become symmetrical to the pattern of the pulse rate when it wasraised, then the output of pulses is stopped.

In the above-mentioned configuration, however, the frictional load ofthe mechanism for generating and transmitting a driving force is changedfrom the initial design value due to a great change of the ambienttemperature and degradation of the mechanism parts with time.Consequently, problems arise; for example, the pick-up cannot be movedand it takes more time to move the pick-up to a target position on thedisk arise. These problems can be solved by detecting the step-out ofthe stepping motor using a rotation detecting means being comprised of,for example, an encoder, and when a step-out is detected, the generatedtorque is controlled by a means of changing the motor driving voltageand so on. The above-mentioned problems can also be solved by drivingthe stepping motor at a slow pulse rate. However, the means fordetecting step-out is expensive. And in the case that the pulse rate islowered, another problem that the accessing performance is degradedarises.

In addition to the pick-up traverse mechanism, the disk apparatusdefined in the twenty-fifth embodiment of the present invention isprovided with a means of detecting the step-out of the stepping motorwithout using any special detector; a means of changing the drivingvoltage and the driving pulse rate of the stepping motor according tothe detection result of the step-out detecting means; and a means ofchanging the driving pulse rate. With such a configuration, the diskapparatus can move the pick-up fast and stably even when the frictionalload of any mechanism is changed.

[Configuration of the Disk apparatus in the Twenty-fifth Embodiment]

Hereunder, a configuration of the twenty-fifth embodiment of the presentinvention will be explained more in detail with reference to theattached drawings.

FIG. 41 is a block diagram for the configuration of the disk apparatusdefined in the twenty-fifth embodiment of the present invention. FIG. 42is a wave form chart indicating a pulse rate pattern used in thetwenty-fifth embodiment.

In FIG. 41, the disk 601 having helically-formed tracks is rotated bythe spindle motor 602. Information is recorded/played back on/from theinformation tracks of the disk 601 via the pick-up 603. The pick-up 603is provided with a lens 604. This lens 604 is provided movably by thefocus actuator and the tracking actuator (not illustrated) incorporatedin the pick-up 603 both in the vertical and horizontal directionsmagnetically. The focus servo means 605 drives the focus actuator sothat the lens 604 is kept away from the disk 601 by a fixed distanceaccording to the focus error signal indicating a displacement value fromthe disk 601.

The tracking servo means 606 drives the tracking actuator so that thelens 604 follows up a given information track on the disk 601 accordingto the tracking error signal indicating a displacement value of the lens601 from the center of the tracks on the disk 601. The stepping motor607 moves the pick-up 603 in the radial direction of the disk 601. Thestepping motor driving means 608 applies a driving voltage to thestepping motor 607. The pick-up position detecting means 609 detects thecurrent position of the pick-up 603 from the address informationincluded in the data read by the pick-up 603. The pulse counting means610 counts the number of pulses for driving the stepping motor 607,which is needed to move the pick-up 603 from the current position of thepick-up 603 detected by the pick-up position detecting means 609 to atarget address entered from external. The pulse rate pattern creatingmeans 611 creates a frequency change (pulse rate) pattern of the inputpulses, entered to the stepping motor driving means 608, according tothe number of pulses counted by the pulse counting means 610.

The driving pulse count detecting means 613 is comprised of a digitalcircuit or a CPU, etc. and used for detecting the number of drivingpulses output from the pulse rate pattern creating means 611. Receivingsignals from the tracking servo means 606, the track crossing detectingmeans 614 detects the number of tracks crossed by the pick-up 303.

The comparing means 615 converts the output of the driving pulse countdetecting means 613 to the number of tracks according to the resolutionof the stepping motor 607 and compares this converted value with thenumber of tracks crossed by the pick-up 303, output from the trackcrossing detecting means 614. The comparing means 615, when it is overthe specified value, decides the difference to be a step-out and outputsa step-out detection signal. The driving voltage variable means 616divides the driving voltage of the stepping motor 607 into n steps (n:an integer of 2 or over) according to the step-out detection signaloutput from the comparing means 615. The feed screw 612 holds thepick-up 603 movably in the radial direction of the disk 601 andtransmits the torque of the stepping motor 607 to the pick-up 603.

[Operation of the Disk Apparatus in the Twenty-fifth Embodiment]

Hereunder, the operation of the disk apparatus defined as explainedabove in the twenty-fifth embodiment of the present invention will beexplained.

The lens 604 is controlled by the focus servo means 605 and the trackingservo means 606 to read information from the disk 601 via the pick-up603. The focus servo means 605 controls the lens 605 so that the lens604 can be kept focused on the disk 601. The tracking servo means 606 iscontrolled by an electromagnetic actuator (not illustrated) so that thelens 604 can keep following up the target track of the disk 601. Whilethe lens 604 follows up the information track of the disk 601, however,the step-out detecting means 650 being comprised of the track crossingdetecting means 614, the driving pulse count detecting means 613, andthe comparing means 615 is stopped.

After this, to access a given track, the current position of the pick-upis detected first. To detect the current position, the data includingthe address information is read from the disk 601 via the pick-up 603.The pick-up position detecting means 609 detects the current position ofthe pick-up 603 from the address information. The pulse counting means610 then counts the number of pulses necessary for moving the pick-upfrom the detected current position to a target track.

After this, the tracking servo means 606 is stopped, then a pulse rateas shown in FIG. 42 is created by the pulse rate pattern creating means611 being comprised of a microcomputer, etc. This pulse rate is outputto the stepping motor driving means 608. The stepping motor drivingmeans 608 drives the stepping motor 607 at the received pulse rate tomove the pick-up 603. After the pick-up 603 reaches a target position,the tracking servo means 606 is started again to record/play backinformation.

While the pick-up 603 is moved, the driving pulse count detecting means613 counts up according to the output of the pulse rate pattern creatingmeans 611. Furthermore, the track crossing detecting means 614 countsthe number of tracks crossed by the lens 604 according to the movementof the pick-up 603. When the stepping motor 607 is rotated synchronouslywith the pulse output from the pulse rate pattern creating means 611,the rotating distance of the stepping motor 607 corresponds to themoving distance of the pick-up 603. Consequently, the output of thedriving pulse count detecting means 613 corresponds to the movingdistance of the pick-up 603 and the track cross detecting means 614outputs a value corresponding to the moving distance of the pick-up 604.The difference between the moving distance of the pick-up 603 and themoving distance of the lens 604 is within the movable range of the lens604 with respect to the pick-up 603.

Next, a case that the stepping motor 607 is desynchronized (stepped out)will be explained. In such a desynchronizing, the driving pulse countdetecting means 613 counts up according to the output of the pulse ratepattern creating means 611. However, because the pick-up 603 is notmoved by a specified distance yet at such a time, the track crossingdetecting means 614 cannot count up the number of tracks crossed by thepick-up 603 any longer. The difference between the output of the drivingpulse count detecting means 613 and the output of the track crossingdetecting means 614 thus becomes a great value. This output differenceis measured by the comparing means 615 and when the difference is great,it is decided that the stepping motor is stepped out. When the comparingmeans 615 decides the stepping motor to be stepped out, the comparingmeans 615 outputs a step-out detection signal to the driving voltagevariable means 616. Receiving the step-out detection signal, the drivingvoltage variable means 616 raises the voltage for driving the steppingmotor 607. Consequently, the torque generated in the stepping motor 607is increased and the stepping motor 607 is restored from the step-outcaused by a change of the driving load.

Since the disk apparatus defined in the twenty-fifth embodiment isformed as explained above, if the driving load is changed by an ambienttemperature change, degradation of any mechanism part with time, etc.,the step-out of the stepping motor is detected, so that the drivingvoltage of the stepping motor 607 is controlled properly. The diskapparatus defined in the twenty-fifth embodiment can thus transmit theoptimal driving force to the pick-up 603 and move the pick-up 603 fast.

<<Twenty-sixth Embodiment>>

Hereunder, the disk apparatus defined in the twenty-sixth embodiment ofthe present invention will be explained with reference to the attacheddrawings. FIG. 43 is a block diagram for a configuration of the diskapparatus in the twenty-sixth embodiment. In FIG. 43, the sameconfiguration items as those in the twenty-fifth embodiment will begiven the same numerals, omitting redundant explanation.

In FIG. 43, the pulse rate detecting means 617 is being comprised of adigital circuit or a CPU, etc. and used to detect the frequency (pulserate) of the driving pulses output from the pulse rate pattern creatingmeans 611. The track crossing speed detecting means 618 receives signalsfrom the tracking servo means 606 and detects a relative speed of thelens 604 with respect to the tracks according to the number of trackscrossed by the pick-up 603 and the time required for the crossing. Thecomparing means 619 converts the output of the pulse rate detectingmeans 617 to a value of the same unit as that of the track crossingspeed according to the resolution of the stepping motor 607 and comparesthis converted value with the output of the track crossing speeddetecting means 618. The comparing means 619, when the differencebetween the above-mentioned converted value and the output of the trackcrossing speed detecting means 618 reaches a specified value, regardsthe state to be a step-out and outputs a step-out detection signal.

The step-out detecting means 651 is comprised of the pulse ratedetecting means 617, the track crossing speed detecting means 618, andthe comparing means 619. The driving voltage variable means 616 dividesthe driving voltage of the stepping motor 607 into n steps (n: aninteger of 2 or over) according to the step-out detection signal fromthe comparing means 619.

[Operation of the Disk Apparatus in the Twenty-sixth Embodiment]

Hereunder, the operation of the disk apparatus in the twenty-sixthembodiment of the present invention will be explained.

The lens 604 is controlled by the focus servo means 605 and the trackingservo means 606 to read information from the disk 601 via the pick-up603. The focus servo means 605 controls the lens 605 so that the lens604 can be kept focused on the disk 601. The tracking servo means 606 iscontrolled by an electromagnetic actuator (not illustrated) so that thelens 604 can keep following up the target track of the disk 601. Whilethe lens 604 follows up the information track of the disk 601, however,the step-out detecting means 651 being comprised of the track crossingspeed detecting means 618, the pulse rate detecting means 617, and thestep-out detecting means 651 is stopped.

After this, to access a given track, the current position of the pick-upis detected first. To detect the current position, the data includingthe address information is read from the disk 601 via the pick-up 603.The 609 detects the current position of the pick-up 603 from the addressinformation. The pulse counting means 610 then counts the number ofpulses necessary for moving the pick-up from the detected currentposition to a target track.

After this, the tracking servo means 606 is stopped, then a pulse rateas shown in FIG. 42 is created by the pulse rate pattern creating means611 being comprised of a microcomputer, etc. This pulse rate is outputto the stepping motor driving means 608. The stepping motor drivingmeans 608 drives the stepping motor 607 at the received pulse rate tomove the pick-up 603. After the pick-up 603 reaches a target position,the tracking servo means 606 is started again to record/play backinformation.

While the pick-up 603 is moving, the pulse rate detecting means 617detects the speed in the pulse rate shown, for example, in FIG. 42,output from the pulse rate pattern creating means 611. Furthermore, thetrack crossing speed detecting means 618 counts the number of trackscrossed by the pick-up 603 according to the movement of the pick-up 603to detect the speed of the pick-up 603. When the stepping motor 607 isrotated synchronously with the pulse output from the pulse rate patterncreating means 611, the rotation speed of the stepping motor 607corresponds to the moving speed of the pick-up 603. Consequently, theoutput of the pulse rate detecting means 617 corresponds to the movingspeed of the pick-up 603. The output of the track crossing speeddetecting means 618 indicates the moving speed of the lens 604. This iswhy the difference between the moving speed of the pick-up 603 and themoving speed of the lens 604 is controlled within a fixed value.

Next, a case that the stepping motor 607 is desynchronized (stepped out)will be explained.

The pulse rate detecting means 617 detects the speed in the pulsepattern shown in FIG. 42 according to the output of the pulse ratepattern creating means 611. If desynchronizing (step-out) occurs,however, the track crossing speed detecting means 618 detects that thespeed of the lens 604 is reduced almost to 0. Because, the pick-up 603stops and there is no track to be crossed by the lens 604. As a result,the difference between the output of the pulse rate detecting means 617and the output of the track crossing speed detecting means 618 isincreased greatly, the comparing means 619 detects a step-out andoutputs a step-out detection signal to the comparing means 619.Receiving the step-out detection signal, the comparing means 619 raisesthe voltage for driving the stepping motor 607. The torque generated inthe stepping motor 607 is thus increased to restore the stepping motor607 from the step-out caused by a change of the driving load.

Since the disk apparatus in the twenty-sixth embodiment is formed suchway, it is possible to detect a step-out to occur in the stepping motorwhen a driving load change is caused by an ambient temperature change,degradation of mechanism parts with time, etc., so that the drivingvoltage of the stepping motor 607 is controlled properly. Andaccordingly, the disk apparatus in the twenty-sixth embodiment cantransmit the optimal driving force to the pick-up 603 to move thepick-up 603 fast.

<<Twenty-seventh Embodiment>>

Next, the disk apparatus in the twenty-seventh embodiment of the presentinvention will be explained with reference to the attached drawings.FIG. 44 is a block diagram for a configuration of the disk apparatus inthe twenty-seventh embodiment of the present invention. In FIG. 44, thesame configuration items as those in the twenty-fifth embodiment will begiven the same numerals, omitting redundant explanation. FIG. 45indicates a pulse pattern (a) to be entered to the stepping motor 607,current patterns (b) and (d) flowing in the stepping motor 607, and arotation speed (c) pattern of the stepping motor 607 in thetwenty-seventh embodiment.

In FIG. 44, the driving current detecting means 620 detects the currentvolume supplied from the stepping motor driving means 608 to thestepping motor 607. The reference current creating means 621 outputs asignal representing the reference current volume according to thefrequency of the pulses output from the pulse rate pattern creatingmeans 611 and the voltage supplied from the driving voltage variablemeans 616 to the stepping motor 607. The comparing means 622 comparesthe output value of the driving current detecting means 620 with theoutput value of the reference current creating means 621 and when thedifference absolute value exceeds a specified value, the comparing means622 regards it as a step-out and outputs a step-out detection signal tothe driving voltage variable means 616. The driving voltage variablemeans 616 divides the driving voltage of the stepping motor 607 into nsteps (n: an integer of 2 or over) according to the step-out detectionsignal from the comparing means 622 provided in the step-out detectingmeans 652. The step-out detecting means 652 is composed of the drivingcurrent detecting means 620, the reference current creating means 621,and the comparing means 622.

[Operation of the Disk Apparatus in the Twenty-seventh Embodiment]

Next, the operation of the disk apparatus formed as explained above inthe twenty-seventh embodiment of the present invention will beexplained.

The lens 604 is controlled by the focus servo means 605 and the trackingservo means 606 to read information from the disk 601 via the pick-up603. The focus servo means 605 controls the lens 604 so that the lens604 can be kept focused on the disk 601. The tracking servo means 606controls the lens 604 using an electromagnetic actuator so that the lens604 can keep following up the tracks on the disk 601. While the lens 604follows up the tracks on the disk 601, however, the step-out detectingmeans 652 being comprised of the driving current detecting means 620,the reference current creating means 621, and the comparing means 622stops.

After this, the current position of the pick-up 603 is detected toaccess a given track. For this accessing, the data including the addressinformation is read from the disk via the pick-up 603. The pick-upposition detecting means 609 uses the address information to detect thecurrent position of the pick-up 603. The pulse counting means 610 countsthe number of pulses necessary for moving the pick-up 603 from thedetected current position to a target track.

Then, while the tracking servo means 606 stops, the pulse rate patterncreating means 611 being composed of a microcomputer, etc. creates apulse rate as shown in (a) of FIG. 45 and outputs the pulse rate to thestepping motor driving means 608. The stepping motor driving means 608uses the received pulse rate to drive the stepping motor 607 to move thepick-up 603.

When the pick-up 603 reaches the target track, the disk apparatusrestarts the tracking servo means 606 again to record/play backinformation.

(b) of FIG. 45 indicates a current volume flowing in the stepping motor607 on the time axis (horizontal axis) while the pick-up in the traversemechanism in the twenty-seventh embodiment is moving. The currentpattern of the stepping motor 607 shown in (b) of FIG. 45 is for a casein which the stepping motor does not step out.

When V1 is defined as a driving voltage applied to the stepping motor607 by the driving voltage variable means 616, Ea is defined as acounter electromotive voltage generated in the stepping motor 607 anddecided by the rotation speed, and R is defined as a resistance value ofthe stepping motor 607, then the current I represented as (V1−Ea)/R isflown in the stepping motor 607.

In the disk apparatus defined in the twenty-seventh embodiment, thereference current creating means 621 has a table or an expressiondefining the relationship among the resistance value, the rotationspeed, and the counter electromotive voltage of the stepping motor 607beforehand. The reference current creating means 621 counts thereference current according to the output value of the driving voltagevariable means 616 and the pulse rate output from the pulse rate patterncreating means 611 and outputs the counted value.

When the stepping motor 607 is rotating synchronously with the pulsesoutput from the pulse rate pattern creating means 611, both the detectedvalue of the driving current detecting means 620 and the output of thereference current creating means 621 become (V1−Ea)/R, and thisdifference is kept within a fixed value.

Next, a case that the stepping motor 607 is desynchronizing (steppedout) will be explained.

The stepping motor 607 slows down below an instructed value (pulse rate)output from the pulse rate pattern creating means 611 as shown in (c) ofFIG. 45 when a step-out occurs. Because of this, a counter electromotivevoltage Ea′ generated in the stepping motor 607 takes the relations ofEa′<Ea. Thus, a motor current as shown in (d) of FIG. 45 is flown in thestepping motor 607. Consequently, the comparing means 622 detects thestep-out and outputs a step-out detection signal. The driving voltagevariable means 616, when a step-out detection signal is output,increases the voltage for driving the stepping motor 607 and the torquegenerated in the stepping motor 607 to eliminate the step-out errorcaused by a change of the driving load.

Because the disk apparatus is formed such way in the twenty-seventhembodiment, it is possible to detect a step-out to occur in the steppingmotor and to control the driving voltage of the stepping motor 607properly even when a driving load change is caused by an ambienttemperature change, degradation of mechanism parts with time, etc. Andaccordingly, the disk apparatus in the twenty-sixth embodiment of thepresent invention can transmit the optimal driving force to the pick-up603 to move the pick-up 603 fast.

<<Twenty-eighth Embodiment>>

Hereunder, the disk apparatus in the twenty-eighth embodiment of thepresent invention will be explained with reference to the attacheddrawings. FIG. 46 is a block diagram for a configuration of the diskapparatus defined in the twenty-eighth embodiment. FIG. 47 is a flowchart for a step-out detecting operation in the disk apparatus in thetwenty-eighth embodiment. In FIG. 46, the same configuration items asthose in the above-mentioned twenty-fifth embodiment will be given thesame numerals, omitting redundant explanation.

In FIG. 46, the target address storing means 623 stores a target addressentered from external. The arrival address storing means 624 stores thenew address of the pick-up 607 after the pick-up 607 is moved to atarget track. The new address is output from the pick-up positiondetecting means 609. The comparing means 625 compares the output valueof the target address storing means 623 with the output value of thearrival address storing means 624. When the difference exceeds aspecified value, the comparing means 625 regards it as a step-out andoutputs a step-out detection signal. The step-out detecting means 653 iscomprised of the target address storing means 623, the arrival addressstoring means 624, and the comparing means 625.

The driving voltage variable means 616 divides the driving voltage ofthe stepping motor 607 into n steps (n: an integer of 2 or over)according to the step-out detection signal from the comparing means 625provided in the step-up detecting means 653.

When the stepping motor 607 steps out as explained above, the steppingmotor 607 cannot keep the synchronous rotation with the input pulses.Thus, the stepping motor 607 stops. Then, the pick-up 603 also stopsbefore it reaches a target position. On the contrary, when the steppingmotor 607 does not step out, the pick-up 603 reaches the targetposition, so the difference of the lens 604 from the target positionafter the pick-up 603 is moved is kept within the movable range of thelens 604 with respect to the pick-up 603.

This is why the target address is compared with the arrival address todetect the step-out of the stepping motor 607 in the disk apparatus inthe twenty-eighth embodiment.

[Step-out Detection in the Twenty-eighth Embodiment]

Next, how a step-out of the stepping motor 607 will be detected in thedisk apparatus in the twenty-eighth embodiment of the present inventionwill be explained.

The lens 604 is controlled by both the focus servo means 605 and thetracking servo means 606 to read information from the disk 601 via thepick-up 603. The focus servo means 605 controls the lens 604 so that thelens 604 can be kept focused on the disk 601. The tracking servo means606 controls the lens 604 so that the lens 604 can keep following up thetarget track on the disk 601 using an electromagnetic actuator.

Next, the flow chart shown in FIG. 47 indicating a step-out detectingoperation in the disk apparatus defined in the twenty-eighth embodimentwill be explained.

In order to access a given track, the current position of the pick-up603 is detected at first. For this detection, the data including theaddress information is read from the disk 601 via the pick-up 603. Then,the pick-up position detecting means 609 detects the current position ofthe pick-up 603 from the address information (step S601).

The pulse counting 610 counts the number of pulses necessary for movingthe pick-up 603 from the detected current position to a target address(step S602). The target address is stored in the target address storingmeans 623 (step S603).

After this, the tracking servo means 606 is stopped (step S604). Then,the pulse rate pattern creating means 611 being comprised of amicrocomputer, etc. creates a pulse rate as shown in FIG. 42 and outputsthe pulse rate to the stepping motor driving means 608. The steppingmotor driving means 608 then drives the stepping motor 607 at this pulserate to move the pick-up 603 (step S605).

The disk apparatus in the twenty-eighth embodiment generates thespecified number of pulses to move the pick-up 603 by a specifieddistance, then restarts the tracking servo means 606 to make the lens604 follow up the target track of the disk 601 (step S606).

The arrival address of the pick-up 603 is read and stored in the arrivaladdress storing means 624 (step S607).

The comparing means 625 counts the difference of the moving distance ofthe pick-up 603 from the values stored in the target address storingmeans 623 and arrival address storing means 624 (step S608). Thecomparing means 625 then compares the obtained difference of the movingdistance with the reference moving difference, which is a movabledistance of the lens 604. Only when the difference of the movingdistance exceeds the reference value, the comparing means 625 decides itas a step-out (step S609) and outputs a step-out detection signal to thedriving voltage variable means 616 (step S610).

Receiving the step-out detection signal, the driving voltage variablemeans 616 increases the voltage for driving the stepping motor 607.Thus, the torque generated in the stepping motor 607 is increased torestore the stepping motor 607 from the step-out caused by a change ofthe driving load.

Since the disk apparatus defined in the twenty-eighth embodiment isformed as explained above, if the driving load is changed by an ambienttemperature change, degradation of any mechanism part with time, etc.,the step-out of the stepping motor is detected, so that the drivingvoltage of the stepping motor 607 is controlled properly. The diskapparatus defined in the twenty-eighth embodiment can thus transmit theoptimal driving force to the pick-up 603 and move the pick-up 603 fast.

<<Twenty-ninth Embodiment>>

Hereunder, the disk apparatus in the twenty-ninth embodiment of thepresent invention will be explained with reference to the attacheddrawings. FIG. 48 is a block diagram for a configuration of the diskapparatus in the twenty-ninth embodiment. In FIG. 48, the sameconfiguration items as those in the above-mentioned twenty-eighthembodiment will be given the same numerals, omitting redundantexplanation. Only the differences from the disk apparatus in thetwenty-eighth embodiment will thus be explained here.

In FIG. 48, the pulse rate pattern variable means 626 divides the pulserate pattern from the pulse rate pattern creating means 611 into m steps(m: an integer of 2 or over) according to the step-out detection signalfrom the 625.

Hereunder, the disk apparatus formed such way in the twenty-ninthembodiment of the present invention will be explained. In the diskapparatus defined in the twenty-ninth embodiment, there is only adifference from the above-mentioned twenty-eighth embodiment; when astep-out is detected, the speed and acceleration of the pulse rateoutput from the pulse rate pattern creating means 611 are lowered, notincreasing the driving voltage of the stepping motor 607.

FIG. 49 indicates the relationship between pulse rate pattern and torqueof the stepping motor 607 before a step-out is detected in thetwenty-ninth embodiment.

When the stepping motor 607 is driven at the pulse rate pattern K1 shownin (a) of FIG. 49, the torque T1 shown in (b) of FIG. 49 is needed toaccelerate and decelerate the stepping motor 607. Furthermore, while thestepping motor 607 is driven by a frictional load, a fixed torque T2 asshown in (c) of FIG. 49 is needed.

When the stepping motor 607 is driven at a fixed voltage, the torque T3generated in the stepping motor 607 is lowered as the rotation speed ofthe stepping motor 607 is raised, as shown in (d) of FIG. 49. When thefrictional load is changed, the torque T3 generated in the steppingmotor 607 becomes less than the total of the torque T1 needed foracceleration and the frictional load torque T2, then a torque shortageoccurs, which causes the stepping motor 607 to step out.

FIG. 50 indicates the relationship between the pulse pattern K2 and thetorque after a step-out is detected in the twenty-ninth embodiment.

When a step-out is detected, the speed and acceleration of the pulserate pattern output from the pulse rate pattern creating means 611 arelowered below the pulse rate pattern K1 shown in (a) of FIG. 49, justlike the pulse rate pattern K2 shown in (a) of FIG. 50. When theacceleration is lowered such way, the torque T1′ needed to acceleratethe pick-up movement can also be lowered. In addition, when the maximumspeed is lowered, the torque T3′ generated by the stepping motor isincreased significantly as shown in (d) of FIG. 50. In this generatedtorque T3′, therefore, the margin of the total of the torque T1′ neededfor acceleration and the frictional load torque T2′ is increased. Thisis why the disk apparatus in the twenty-ninth embodiment can preventstep-out.

Although the step-out detecting means 653 shown in the above-mentionedtwenty-eighth embodiment is used for detecting the step-out in thetwenty-ninth embodiment, the present invention is not limited only tothis configuration. For example, any of the step-out detecting means650, 651, and 652 used in the twenty-fifth to twenty-seventh embodimentsmay be used to obtain the same effect as that in the twenty-ninthembodiment.

Since the disk apparatus defined in the twenty-ninth embodiment isformed as explained above, if the driving load is changed by an ambienttemperature change, degradation of any mechanism part with time, etc.,the step-out of the stepping motor is detected, so that the drivingvoltage of the stepping motor 607 is controlled properly. The diskapparatus defined in the twenty-ninth embodiment can thus transmit theoptimal driving force to the pick-up 603 and move the pick-up 603 to thetarget position certainly.

<<Thirtieth Embodiment>>

Next, the disk apparatus in the thirtieth embodiment of the presentinvention will be explained with reference to the attached drawings.

In the twenty-fifth to twenty-eighth embodiments of the presentinvention, each time a step-out is detected, the driving voltage of thestepping motor 607 is raised to increase the torque generation in thestepping motor 607 to cope with the change of the frictional load ofrotation. In such a configuration, however, when the driving voltage israised, the temperature in the stepping motor 607 also risessignificantly. Furthermore, in the disk apparatus in the twenty-ninthembodiment, each time a step-out is detected, the speed and accelerationin the pulse rate of the stepping motor 607 are lowered to lower thenecessary torque for rotation to cope with changes of the frictionalload. In this configuration, as the pulse rate is lowered, the moving ofthe pick-up 603 is delayed significantly.

The disk apparatus in the thirtieth embodiment is provided to solve suchthe problems.

Hereunder, the thirtieth embodiment of the present invention will beexplained with reference to the attached drawings. FIG. 51 is a blockdiagram for a configuration of the disk apparatus in the thirtiethembodiment of the present invention. In FIG. 51, the same configurationitems as those in the above-mentioned twenty-eighth embodiment will begiven the same numerals, omitting redundant explanation.

Hereunder, only the differences from the disk apparatus in thetwenty-eighth embodiment will be explained.

In FIG. 51, the step-out count deciding means 627 counts the number ofstep-out times according to the step-out detection signal output fromthe comparing means 625 provided in the step-out detecting means 653.The comparing means 625 is provided with a step-out count storing means(not illustrated) and used to store the number of step-out times in thestep-out count storing means. The step-out count deciding means 627controls the driving voltage variable means 616 and the pulse ratepattern variable means 626 according to the step-out detection signaland the output from the step-out count storing means.

In the disk apparatus defined in the thirtieth embodiment, the drivingvoltage variable means 616 and the pulse rate pattern variable means 626are controlled by the step-out count deciding means 627, not by theoutput from the comparing means 625.

FIG. 52 is a flow chart indicating the operation of the step-out countdeciding means 627 for controlling the driving voltage variable means616 and the pulse rate pattern variable means 626. FIG. 53 is a graphindicating a pulse rate pattern created and output by the pulse ratepattern creating means 611 in the thirtieth embodiment.

Next, the operation of the disk apparatus formed as explained above inthe thirtieth embodiment of the present invention will be explained withreference to FIG. 52.

The operation is completely the same as that described in theabove-mentioned twenty-eighth embodiment until the pick-up 603 is moved(step S601) and it is decided whether or not the stepping motor stepsout.

When the pick-up 603 is moved, the step-out count deciding means 627checks whether or not a step-out is detected (step S602). If no step-outis detected, the movement of the pick-up 603 is ended. If a step-out isdetected, the number of step-out errors is counted (step S603). Thepulse rate pattern variable means 626 thus sets the pulse rate patternK3 shown in (c) of FIG. 53. The pulse rate pattern variable means 626sets the pulse rate pattern K3 so that the maximum speed andacceleration are lowered enough below those in the pulse rate pattern Kl(initial value) shown in (a) of FIG. 53 (step S604). Then, the pick-up603 is moved only by the remaining distance (step S605).

If a step-out is detected, the following processing is executedaccording to the number of step-out times.

If the step-out count is less than N1 (N1: an integer of 1 or over)(step S606), the pulse rate pattern is set to K1 again and the movementof the pick-up 603 is ended (step S607).

If the step-out count is N1 or over and less than N2 (N2: an integer ofN1 or over) (step S608), the driving voltage variable means 616 sets thedriving voltage of the stepping motor 607 to h2 (h2>initial value h1).Then, the pulse rate pattern variable means 626 sets the pulse ratepattern to K1 again and ends the movement of the pick-up 603 (stepS607).

If the step-out count is N2 or over and less than N3 (N3: an integer ofN2 or over) (steps S610 and S611), the driving voltage variable means616 returns the driving voltage of the stepping motor 607 to the initialvalue h1 (step S612). Then, the pulse rate pattern variable means 626sets the pulse rate pattern to K2 shown in (b) of FIG. 53 to end themovement of the pick-up 603 (step S613). The pulse rate pattern K2indicates that the maximum speed and acceleration are between pulse ratepatterns K1 and K2.

If the step-out count is N3 or over (step S610), the movement of thepick-up 603 is ended while the pulse rate pattern K3 set in step S4 isleft as is.

Since the disk apparatus defined in the thirtieth embodiment is formedas explained above, if the driving load is changed by an ambienttemperature change, degradation of any mechanism part with time, etc.,the step-out of the stepping motor is detected, so that the drivingvoltage of the stepping motor 607 is controlled properly. The diskapparatus defined in the twenty-ninth embodiment can thus transmit theoptimal driving force to the pick-up 603 and move the pick-up 603 fastto a target position certainly while keeping the temperature of thestepping motor 607 fixedly.

Although the step-out detecting means 653 shown in the above-mentionedthirtieth embodiment is used for detecting step-out in the thirtiethembodiment, the present invention is not limited only to thisconfiguration. For example, any of the step-out detecting means 650,651, and 652 used in the twenty-fifth to twenty-seventh embodiments maybe used to obtain the same effect as that in the thirtieth embodiment.

Although the driving voltage can be changed over in 2 steps and thepulse rate pattern can be changed over in 3 steps in the thirtiethembodiment, the number of steps for changing over those may be furtherincreased to improve the stability and speed of the pick-up 603 moresignificantly.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artto which the present invention pertains, after having read theabove-mentioned disclosure. Accordingly, it is intended that theappended claims be interpreted as covering all alterations andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:
 1. A disk drive apparatus comprising: a disk havinghelically-formed or concentric circle-like formed tracks; a spindlemotor for controlling a rotation speed of said disk; a pick-up forrecording or playing back information on or from said disk, the pick-uphaving a lens; servo means for making the lens of said pick-up follow upsaid tracks of said disk; a stepping motor for moving said pick-up in aradial direction of said disk; a system controller for outputtingcommand signals according to the rotation speed of said spindle motor;and stepping motor control means for controlling said stepping motor bychanging an inclination of a rising part and a falling part in awaveform of a drive current of said stepping motor according to saidcommand signals received to change a moving speed of said pick-up.
 2. Amethod for controlling a stepping motor by dividing a basic step angleof said stepping motor into n angles (n: an integer of 2 or over),wherein when said stepping motor is rotated and rested at a mechanicalinstability point in a position other than said basic step angle, thedirection or the volume of a driving current for resting said steppingmotor is changed according to the rotating direction of said steppingmotor until said stepping motor reaches said mechanical instabilitypoint.
 3. Then method for controlling a stepping motor in accordancewith claim 2, wherein the volume of said driving current for restingsaid stepping motor at a mechanical instability point in a positionother than said basic step angle is varied.
 4. The method forcontrolling a stepping motor in accordance with claim 2, wherein aftersaid stepping motor is rotated and rested, said stepping motor drivingcurrent is reduced gradually in proportion to time so that the rotatingangle of said stepping motor at rest is kept with a lower current thanthe current volume required for rotating.
 5. The method for controllinga stepping motor in accordance with claim 4, wherein said current volumefor keeping the rotating angle of said stepping motor at rest is varied.6. The method for controlling a stepping motor in accordance with claim2, wherein when said stepping motor is at rest at a mechanicalinstability position, said driving current volume is increased more thanthat when said stepping motor is at rest at a mechanical stabilityposition.
 7. A disk apparatus comprising: a disk having helically orconcentric circle-like formed tracks; a spindle motor for controlling arotation speed of said disk; a pick-up for recording or playing backinformation on or from said disk, the pick-up having a lens; servo meansfor making the lens of said pick-up follow up said tracks of said disk,and for outputting an error signal when said pick-up is vibrated over aspecified value; a stepping motor for moving said pick-up in a radialdirection of said disk; a system controller for outputting a firstcommand signal when detecting that said error signal output by saidservo means has exceeded the specified value, and for outputting asecond command signal when detecting that said error signal has notexceeded the specified value for a fixed time period; and stepping motorcontrol means for controlling said stepping motor by increasing adriving current volume for keeping a rotating angle of said steppingmotor after receiving said first command signal, and for controllingsaid stepping motor by decreasing said driving current volume forkeeping the rotating angle of said stepping motor after receiving saidsecond command signal.
 8. A disk apparatus comprising: a stepping motor;stepping motor controlling means for controlling said stepping motor bydividing a basic step angle of said stepping motor into n angles (n: aninteger of 2 or over), wherein when said stepping motor is rotated andrested at a mechanical instability point in a position other than saidbasic step angle, the direction or the volume of said driving currentfor resting said stepping motor is changed according to the rotatingdirection of said stepping motor until said stepping motor reaches saidmechanical instability point.
 9. The disk apparatus according to claim8, wherein the volume of said driving current for resting said steppingmotor at a mechanical instability point in a position other than saidbasic step angle is varied.
 10. The disk apparatus according to claim 8,wherein after said stepping motor is rotated and rested, said steppingmotor driving current is reduced gradually in proportion to the time sothat the rotating angle of said stepping motor at rest is kept with alower current than the current volume required for rotating.
 11. Thedisk apparatus according to claim 10, wherein said current volume forkeeping the rotating angle of said stepping motor at rest is varied. 12.The disk apparatus according to claim 8, wherein when said steppingmotor is at rest at a mechanical instability position, said currentvolume is increased more than that when said stepping motor is at restat a mechanical stability position.